OK so I am a dork, and I neglected to remember that you can't use both I2C on UART0 as well as the UART function.....

I need to access (multiplex) a number of serial communication devices to the same (UART) port so plan on doing that with analog switches (and control lines for routing).

So now what I am thinking, is to use an inexpensive MSP like 2132 as a I2C/UART bridge, meaning that the main MSP will query it over the I2C, the 2132 will route the query to the relevant peripheral over UART (and using the relevant analog switch configuration), and send back the reply to the master MSP.

Sound like an OK design?

Also, is it possible to take the master clock from the main MSP and this way save a crystal on the 2132?

Thanks for your comments on this idea/design.....
------------------------------------



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Hi merapcb,

> I need to access (multiplex) a number of serial communication
> devices to the same (UART) port so plan on doing that with analog
> switches (and control lines for routing).

Your analog switches solution will only help if there is only one uart port sending data at once, or if you use hardware flow control.
You could instad use an MSP and have multiple software UARTs so all ports can be received at the same time. I just implemented this solution with 8 UARTs (RX only) and it works flawlessly. In my case the low datarate of only 300bps on each port (althought constantly transmitting data) was low enought not to arise any time constraint issues. Upon reception of a complete packed on each of the uarts, the packed was checked for integrity (simple XOR CRC) and then retransmitted throught the hardware 115200bps UART.

> Also, is it possible to take the master clock from the main MSP and
> this way save a crystal on the 2132?

As I rememberm the XT OUT pin can drive one CMOS gate when there is a clock being fed to the XTIN pin, but I don't know it this is true when using a crystal.
But the alternative should be as simple as outputting the corresponding MCLK, SMCLK or ACLK signal (using the atlernate function of the respective I/O pin) and feeding it into the other chips XTIN input. I've not tried it and I'm not absolutely sure of the voltage level compatibilities of the XTIN input when not using a crystal. You'd have to check that.

Regards,
Michael K.

--- In m...@yahoogroups.com, "merapcb" wrote:
> OK so I am a dork, and I neglected to remember that you can't use both I2C on UART0 as well as the UART function.....
>
> I need to access (multiplex) a number of serial communication devices to the same (UART) port so plan on doing that with analog switches (and control lines for routing).
>
> So now what I am thinking, is to use an inexpensive MSP like 2132 as a I2C/UART bridge, meaning that the main MSP will query it over the I2C, the 2132 will route the query to the relevant peripheral over UART (and using the relevant analog switch configuration), and send back the reply to the master MSP.
>
> Sound like an OK design?
>
> Also, is it possible to take the master clock from the main MSP and this way save a crystal on the 2132?
>
> Thanks for your comments on this idea/design.....
>
------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

--- In m...@yahoogroups.com, "tintronic" wrote:
>

>
> Your analog switches solution will only help if there is only one uart port sending data at once, or if you use hardware flow control.
> You could instad use an MSP and have multiple software UARTs so all ports can be received at the same time. I just implemented this solution with 8 UARTs (RX only) and it works flawlessly. In my case the low datarate of only 300bps on each port (althought constantly transmitting data) was low enought not to arise any time constraint issues. Upon reception of a complete packed on each of the uarts, the packed was checked for integrity (simple XOR CRC) and then retransmitted throught the hardware 115200bps UART.
>

Yes, basically all are slave devices so the "Master" MSP can chose when to poll them.

Regarding clock, I don't know, probably better just to throw in another crystal at the moment.... :-)
------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Do these have to be serial comms devices? ie Are they devices that you
have no control over? If you have control over them there are simpler
ways to overcome this. If not then it depends largely on how many of
them there are, what baud rates they are running at, and how many
different baud rates there are, as to how best to go about it. To some
extent packet size may also have an effect, as will full duplex or half
duplex operation, since you will need to buffer data if you wish to
handle multiple channels simulateously, and will need double the buffers
and buffer management if you want to run full duplex.

Depending on these factors, if you didn't have too many channels, large
data packets or full duplex, with a hardware UART, 8k of Flash and 512
bytes of RAM plus 20 other I/O pins and 5 timer channels the 2132 could
probably handle this, so don't be so vague if you want accurate advice.

Al

merapcb wrote:
> OK so I am a dork, and I neglected to remember that you can't use
> both I2C on UART0 as well as the UART function.....
>
> I need to access (multiplex) a number of serial communication devices
> to the same (UART) port so plan on doing that with analog switches
> (and control lines for routing).
>
> So now what I am thinking, is to use an inexpensive MSP like 2132 as
> a I2C/UART bridge, meaning that the main MSP will query it over the
> I2C, the 2132 will route the query to the relevant peripheral over
> UART (and using the relevant analog switch configuration), and send
> back the reply to the master MSP.
>
> Sound like an OK design?
>
> Also, is it possible to take the master clock from the main MSP and
> this way save a crystal on the 2132?
>
> Thanks for your comments on this idea/design.....
> ------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

--- In m...@yahoogroups.com, OneStone wrote:
>
> Do these have to be serial comms devices? ie Are they devices that you
> have no control over? If you have control over them there are simpler
> ways to overcome this. If not then it depends largely on how many of
> them there are, what baud rates they are running at, and how many
> different baud rates there are, as to how best to go about it. To some
> extent packet size may also have an effect, as will full duplex or half
> duplex operation, since you will need to buffer data if you wish to
> handle multiple channels simulateously, and will need double the buffers
> and buffer management if you want to run full duplex.
>
> Depending on these factors, if you didn't have too many channels, large
> data packets or full duplex, with a hardware UART, 8k of Flash and 512
> bytes of RAM plus 20 other I/O pins and 5 timer channels the 2132 could
> probably handle this, so don't be so vague if you want accurate advice.
>
> Al
>
Sorry, Al. No intention to be vague. Very sorry.

All devices are under my control (not to mean I make them) and they all are on 19,200bps. They are all "slaves" in that they have to be queried. So that makes them half duplex.

What I figured is that with two dual analog switch ICs and two control lines (because you always switch Tx and Rx together) I could use a single UART on the 2132 and then from there over I2C to the main MSP. Rather, the master MSP will send a I2C message with the device it would like to query and the query string, and the 2132 would switch the switches to route the UART to that device, send the query, get the reply, and send it back to the master MSP over I2C.

Hope the intention is clearer now.

Not sure what you mean by the 20 other I/O pins.
------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Why bother with a second micro? It seems pointless to me. You still
haven't said how many devices you plan to have talking to the micro, but
lets assume no more than eight, and more than 4. If less than 4 you can
use a 4052 dual 4:1 mux rather than a pair of 8:1's, which are
physically smaller and cheaper than a dual 8:1. use a pair of 4051's. In
fact you can run 3 if you want, one serving as the chip select. they are
cheap and come in small packages. Then you only need 4 signals in total,
3 to select the multiplexer channel. And these can simply count from
0-7, and 1 to strobe the enable pin on the mux used for Chip select.
This would have its 8 outputs tied one to each of the slaves. the rest
is easy, no need for another micro to hanlde this simple function. as I
said depending on the complexity of the rest of the application you
could handle this with a 2132. In fact you could handle this with a 2012
if this was all it had to do. As for the 20 I/O pins you can run a UART
on apair of I/O pins, one for TX, one for RX. It's easier if they have
interrupt on change, so ports 1 & 2. Even though you don't have all the
dedicated timers by using a fast crystal and a 32 bit clock extender you
can, with a bit of care, share just 1 timer across multiple software uarts.

Cheers

Al

merapcb wrote:
> --- In m...@yahoogroups.com, OneStone wrote:
>> Do these have to be serial comms devices? ie Are they devices that you
>> have no control over? If you have control over them there are simpler
>> ways to overcome this. If not then it depends largely on how many of
>> them there are, what baud rates they are running at, and how many
>> different baud rates there are, as to how best to go about it. To some
>> extent packet size may also have an effect, as will full duplex or half
>> duplex operation, since you will need to buffer data if you wish to
>> handle multiple channels simulateously, and will need double the buffers
>> and buffer management if you want to run full duplex.
>>
>> Depending on these factors, if you didn't have too many channels, large
>> data packets or full duplex, with a hardware UART, 8k of Flash and 512
>> bytes of RAM plus 20 other I/O pins and 5 timer channels the 2132 could
>> probably handle this, so don't be so vague if you want accurate advice.
>>
>> Al
>>
> Sorry, Al. No intention to be vague. Very sorry.
>
> All devices are under my control (not to mean I make them) and they all are on 19,200bps. They are all "slaves" in that they have to be queried. So that makes them half duplex.
>
> What I figured is that with two dual analog switch ICs and two control lines (because you always switch Tx and Rx together) I could use a single UART on the 2132 and then from there over I2C to the main MSP. Rather, the master MSP will send a I2C message with the device it would like to query and the query string, and the 2132 would switch the switches to route the UART to that device, send the query, get the reply, and send it back to the master MSP over I2C.
>
> Hope the intention is clearer now.
>
> Not sure what you mean by the 20 other I/O pins.
> ------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

--- In m...@yahoogroups.com, OneStone wrote:
>
> Why bother with a second micro? It seems pointless to me. You still
> haven't said how many devices you plan to have talking to the micro, but
> lets assume no more than eight, and more than 4. If less than 4 you can
> use a 4052 dual 4:1 mux rather than a pair of 8:1's, which are
> physically smaller and cheaper than a dual 8:1. use a pair of 4051's. In
> fact you can run 3 if you want, one serving as the chip select. they are
> cheap and come in small packages. Then you only need 4 signals in total,
> 3 to select the multiplexer channel. And these can simply count from
> 0-7, and 1 to strobe the enable pin on the mux used for Chip select.
> This would have its 8 outputs tied one to each of the slaves. the rest
> is easy, no need for another micro to hanlde this simple function. as I
> said depending on the complexity of the rest of the application you
> could handle this with a 2132. In fact you could handle this with a 2012
> if this was all it had to do. As for the 20 I/O pins you can run a UART
> on apair of I/O pins, one for TX, one for RX. It's easier if they have
> interrupt on change, so ports 1 & 2. Even though you don't have all the
> dedicated timers by using a fast crystal and a 32 bit clock extender you
> can, with a bit of care, share just 1 timer across multiple software uarts.
>
> Cheers
>
> Al
>
I understand what you are saying but the additional micro is required since I don't have a free additional UART on the master MSP. One is running SPI and the other I2C (it's a 169). So that is why I need to "convert" from UART to I2C, it's the only way I can access these serial devices (at least the only way I thought of).

And I have 4 such devices. So I figure I need two TS5A23159.

Yes, I presume all could be bit banged, but: a) I have never done it before, b) I doubt the micro would have the time as it is fairly busy.

Thanks
------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

I'm sorry but what you are saying makes absolutely no sense to me. Sure
I get what you have, a 169, running 1? SPI device and 1? I2C device, you
don't say how many, then you have 4 external devices with UARTS. Okay
I'd opt for a single 4052 anyway, its a dual 4:1, but that's a moot
point. Your cramming 4 channels into a shared pipe, which is okay, then
cramming them again down a single shared I2C pipe, which will require
quite a bit of overhead from the master anyway. this seems a less than
efficient way to do things. The first thing I'd do is get away from the
169, but if you're stuck with it, and you shouldn't be if you're in the
hardware design stage, then sit and think carefully about the other
components, why the mix of SPI and I2C, is it necessary, how much
sharing is going on already on those lines? The 169 has a lot of I/o,
and a damned good Timer B that can single handedly implement 4 very nice
Uarts, although you might have to get a bit kludgy with the 4th, since
there are only 7 channels. I believe this will be far more efficient
than what you are planning, and less overhead for the micro.

Al

merapcb wrote:
> --- In m...@yahoogroups.com, OneStone wrote:
>> Why bother with a second micro? It seems pointless to me. You still
>> haven't said how many devices you plan to have talking to the
>> micro, but lets assume no more than eight, and more than 4. If less
>> than 4 you can use a 4052 dual 4:1 mux rather than a pair of 8:1's,
>> which are physically smaller and cheaper than a dual 8:1. use a
>> pair of 4051's. In fact you can run 3 if you want, one serving as
>> the chip select. they are cheap and come in small packages. Then
>> you only need 4 signals in total, 3 to select the multiplexer
>> channel. And these can simply count from 0-7, and 1 to strobe the
>> enable pin on the mux used for Chip select. This would have its 8
>> outputs tied one to each of the slaves. the rest is easy, no need
>> for another micro to hanlde this simple function. as I said
>> depending on the complexity of the rest of the application you
>> could handle this with a 2132. In fact you could handle this with a
>> 2012 if this was all it had to do. As for the 20 I/O pins you can
>> run a UART on apair of I/O pins, one for TX, one for RX. It's
>> easier if they have interrupt on change, so ports 1 & 2. Even
>> though you don't have all the dedicated timers by using a fast
>> crystal and a 32 bit clock extender you can, with a bit of care,
>> share just 1 timer across multiple software uarts.
>>
>> Cheers
>>
>> Al
>>
> I understand what you are saying but the additional micro is required
> since I don't have a free additional UART on the master MSP. One is
> running SPI and the other I2C (it's a 169). So that is why I need to
> "convert" from UART to I2C, it's the only way I can access these
> serial devices (at least the only way I thought of).
>
> And I have 4 such devices. So I figure I need two TS5A23159.
>
> Yes, I presume all could be bit banged, but: a) I have never done it
> before, b) I doubt the micro would have the time as it is fairly
> busy.
>
> Thanks
> ------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

--- In m...@yahoogroups.com, OneStone wrote:
>
> I'm sorry but what you are saying makes absolutely no sense to me. Sure
> I get what you have, a 169, running 1? SPI device and 1? I2C device, you
> don't say how many, then you have 4 external devices with UARTS. Okay
> I'd opt for a single 4052 anyway, its a dual 4:1, but that's a moot
> point. Your cramming 4 channels into a shared pipe, which is okay, then
> cramming them again down a single shared I2C pipe, which will require
> quite a bit of overhead from the master anyway. this seems a less than
> efficient way to do things. The first thing I'd do is get away from the
> 169, but if you're stuck with it, and you shouldn't be if you're in the
> hardware design stage, then sit and think carefully about the other
> components, why the mix of SPI and I2C, is it necessary, how much
> sharing is going on already on those lines? The 169 has a lot of I/o,
> and a damned good Timer B that can single handedly implement 4 very nice
> Uarts, although you might have to get a bit kludgy with the 4th, since
> there are only 7 channels. I believe this will be far more efficient
> than what you are planning, and less overhead for the micro.
>
> Al
>

OK, so you are saying mux/demux them in to a single software UART.... (at least I think that is what you are saying :-)

Well no, actually you are saying implement 4 software UARTS, but hey if it's only one device *at a time* I need to talk with, I guess one software UART would do and mux/demux the Rx/Tx signals, right?

OK it is finally sinking in.... if I can bit bang a single software UART, I can use your 4052.... (pity, I liked the 1:3 TS5A3359 I just found! ha)

And yes, away from the 169.... far far away.... :-) But, not possible at the moment due to other dependencies. So that's why all of this. Else, I have my eye on a F5x or F24x with plenty of UARTs to go around...
Thanks
------------------------------------

______________________________
Stellaris® MCU Family: New Parts, New Package, New Price.


(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

If the OP's hardware is already done maybe the best solution is muxing the serial
lines. I would go for a 3V compatible 4052 as All pointed out. The TS5A23159 is a
cute device but more expensive, single supplier (4052 alike you find in baskets on
fish market) and demands 3 devices to handle 4 channels (if you need to switch
both TX and RX lines).
If the hardware is still under test/development then consider changing all....

-Augusto

On Seg 17/08/09 15:33 , OneStone o...@bigpond.net.au sent:
> I'm sorry but what you are saying makes absolutely no sense to me.
> Sure
> I get what you have, a 169, running 1? SPI device and 1? I2C device,
> you
> don't say how many, then you have 4 external devices with UARTS.
> Okay
> I'd opt for a single 4052 anyway, its a dual 4:1, but that's a moot
> point. Your cramming 4 channels into a shared pipe, which is okay,
> then
> cramming them again down a single shared I2C pipe, which will
> require
> quite a bit of overhead from the master anyway. this seems a less
> than
> efficient way to do things. The first thing I'd do is get away from
> the
> 169, but if you're stuck with it, and you shouldn't be if you're in
> the
> hardware design stage, then sit and think carefully about the other
> components, why the mix of SPI and I2C, is it necessary, how much
> sharing is going on already on those lines? The 169 has a lot of
> I/o,
> and a damned good Timer B that can single handedly implement 4 very
> nice
> Uarts, although you might have to get a bit kludgy with the 4th,
> since
> there are only 7 channels. I believe this will be far more efficient
>
> than what you are planning, and less overhead for the micro.
> Al
> merapcb wrote:
> > --- In m...@yahoogroups.com, OneStone wrote:
> >> Why bother with a second micro? It seems pointless to me. You
> still
> >> haven't said how many devices you plan to have talking to the
> >> micro, but lets assume no more than eight, and more than 4. If
> less
> >> than 4 you can use a 4052 dual 4:1 mux rather than a pair of
> 8:1's,
> >> which are physically smaller and cheaper than a dual 8:1. use a
> >> pair of 4051's. In fact you can run 3 if you want, one serving as
> >> the chip select. they are cheap and come in small packages. Then
> >> you only need 4 signals in total, 3 to select the multiplexer
> >> channel. And these can simply count from 0-7, and 1 to strobe the
> >> enable pin on the mux used for Chip select. This would have its 8
> >> outputs tied one to each of the slaves. the rest is easy, no need
> >> for another micro to hanlde this simple function. as I said
> >> depending on the complexity of the rest of the application you
> >> could handle this with a 2132. In fact you could handle this with
> a
> >> 2012 if this was all it had to do. As for the 20 I/O pins you can
> >> run a UART on apair of I/O pins, one for TX, one for RX. It's
> >> easier if they have interrupt on change, so ports 1 & 2. Even
> >> though you don't have all the dedicated timers by using a fast
> >> crystal and a 32 bit clock extender you can, with a bit of care,
> >> share just 1 timer across multiple software uarts.
> >>
> >> Cheers
> >>
> >> Al
> >>
> >
> >
> > I understand what you are saying but the additional micro is
> required
> > since I don't have a free additional UART on the master MSP. One
> is
> > running SPI and the other I2C (it's a 169). So that is why I need
> to
> > "convert" from UART to I2C, it's the only way I can access these
> > serial devices (at least the only way I thought of).
> >
> > And I have 4 such devices. So I figure I need two TS5A23159.
> >
> > Yes, I presume all could be bit banged, but: a) I have never done
> it
> > before, b) I doubt the micro would have the time as it is fairly
> > busy.
> >
> > Thanks
> >
> >
> >
> >
> > ------------------------------------
> >
> >
> >
> >



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

On that note, you might also consider changing the I2C device (or devices? usually an EEPROM?) for an SPI version of the same device. Furthermore, the SPI and UART signals of both USARTs on the 169 are on different pins. You could change the configuration of the USART between UART and SPI depending on what device you need to communicate with.
It's quite simple to bitbang an SPI, so you might free the USART hardware for UART operation.

But I can understand the use of an extra MSP. For one, it might be academically interesting (not sure if you are a student) and it helps breaking down the software into less interacting and time consuming/racing functions, which might significantly reduce the developing time if you have not much experience or if you are unsure if you can cram all the functions into a single MSP. Efficiency is, after all, dependent on the perspective you are measuring it from. You might use one single MSP more efficiently, but the cost of the time spent developing the code might make it less efficient than a mayor cost in hardware would.

If you go with the additional MSP solution, I'd use SPI instead of I2C, since it's far more simple, can be 10 times as fast (4MHz v/s 400kHz), and will probably take you far less time to implement and debug (less overhead).

Regards,
Michael K.

--- In m...@yahoogroups.com, OneStone wrote:
>
> I'm sorry but what you are saying makes absolutely no sense to me. Sure
> I get what you have, a 169, running 1? SPI device and 1? I2C device, you
> don't say how many, then you have 4 external devices with UARTS. Okay
> I'd opt for a single 4052 anyway, its a dual 4:1, but that's a moot
> point. Your cramming 4 channels into a shared pipe, which is okay, then
> cramming them again down a single shared I2C pipe, which will require
> quite a bit of overhead from the master anyway. this seems a less than
> efficient way to do things. The first thing I'd do is get away from the
> 169, but if you're stuck with it, and you shouldn't be if you're in the
> hardware design stage, then sit and think carefully about the other
> components, why the mix of SPI and I2C, is it necessary, how much
> sharing is going on already on those lines? The 169 has a lot of I/o,
> and a damned good Timer B that can single handedly implement 4 very nice
> Uarts, although you might have to get a bit kludgy with the 4th, since
> there are only 7 channels. I believe this will be far more efficient
> than what you are planning, and less overhead for the micro.
>
> Al
>
> merapcb wrote:
> > --- In m...@yahoogroups.com, OneStone wrote:
> >> Why bother with a second micro? It seems pointless to me. You still
> >> haven't said how many devices you plan to have talking to the
> >> micro, but lets assume no more than eight, and more than 4. If less
> >> than 4 you can use a 4052 dual 4:1 mux rather than a pair of 8:1's,
> >> which are physically smaller and cheaper than a dual 8:1. use a
> >> pair of 4051's. In fact you can run 3 if you want, one serving as
> >> the chip select. they are cheap and come in small packages. Then
> >> you only need 4 signals in total, 3 to select the multiplexer
> >> channel. And these can simply count from 0-7, and 1 to strobe the
> >> enable pin on the mux used for Chip select. This would have its 8
> >> outputs tied one to each of the slaves. the rest is easy, no need
> >> for another micro to hanlde this simple function. as I said
> >> depending on the complexity of the rest of the application you
> >> could handle this with a 2132. In fact you could handle this with a
> >> 2012 if this was all it had to do. As for the 20 I/O pins you can
> >> run a UART on apair of I/O pins, one for TX, one for RX. It's
> >> easier if they have interrupt on change, so ports 1 & 2. Even
> >> though you don't have all the dedicated timers by using a fast
> >> crystal and a 32 bit clock extender you can, with a bit of care,
> >> share just 1 timer across multiple software uarts.
> >>
> >> Cheers
> >>
> >> Al
> >>
> >
> >
> > I understand what you are saying but the additional micro is required
> > since I don't have a free additional UART on the master MSP. One is
> > running SPI and the other I2C (it's a 169). So that is why I need to
> > "convert" from UART to I2C, it's the only way I can access these
> > serial devices (at least the only way I thought of).
> >
> > And I have 4 such devices. So I figure I need two TS5A23159.
> >
> > Yes, I presume all could be bit banged, but: a) I have never done it
> > before, b) I doubt the micro would have the time as it is fairly
> > busy.
> >
> > Thanks
> >
> >
> >
> >
> > ------------------------------------
> >
> >
> >
> >



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

>
> OK it is finally sinking in.... if I can bit bang a single software UART, I can use your 4052.... (pity, I liked the 1:3 TS5A3359 I just found! ha)
>

Regardless of all the other architectural options being thrown around, I'd like to make one point... perhaps in the form of a question to the more experienced folk on here.

If I need to "switch" logic paths to/from a set of external devices, why would I choose to use an analog like the 4051/4052/4053 family? Wouldn't a set of data selectors/demuxes ('151, '153, '138, etc) be the purer design choice? I recall years ago, the FET analog switches were associated with latchup problems, ESD sensitivities, etc.

Wouldn't you prefer logic gates to FET switches for logic steering?

Dave
------------------------------------



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Just an idea that might be useful: Since all the devices are slaves, if you use one TTL-232 driver for each slave, you can group all the RX signal using a big AND gate or a combination of AND gates. Since RX line is on a logic '1' while idle, any RX line that goes down to zero will produce a zero on the output of the AND gate (or array of gates). You would then only need a digital mux for the TX part (or you could do it with OR gates depending on how many slaves we're talking about).

I'm curious about the analog switch/mux you plan to use. Did you make sure they support the whole voltage range of the RS-232 standard? I suppose your UART slaves are RS-232 because you talk about an analog switch.

Regards,
Michael K.

--- In m...@yahoogroups.com, "merapcb" wrote:
>
> --- In m...@yahoogroups.com, OneStone wrote:
> >
> > Do these have to be serial comms devices? ie Are they devices that you
> > have no control over? If you have control over them there are simpler
> > ways to overcome this. If not then it depends largely on how many of
> > them there are, what baud rates they are running at, and how many
> > different baud rates there are, as to how best to go about it. To some
> > extent packet size may also have an effect, as will full duplex or half
> > duplex operation, since you will need to buffer data if you wish to
> > handle multiple channels simulateously, and will need double the buffers
> > and buffer management if you want to run full duplex.
> >
> > Depending on these factors, if you didn't have too many channels, large
> > data packets or full duplex, with a hardware UART, 8k of Flash and 512
> > bytes of RAM plus 20 other I/O pins and 5 timer channels the 2132 could
> > probably handle this, so don't be so vague if you want accurate advice.
> >
> > Al
> >
> Sorry, Al. No intention to be vague. Very sorry.
>
> All devices are under my control (not to mean I make them) and they all are on 19,200bps. They are all "slaves" in that they have to be queried. So that makes them half duplex.
>
> What I figured is that with two dual analog switch ICs and two control lines (because you always switch Tx and Rx together) I could use a single UART on the 2132 and then from there over I2C to the main MSP. Rather, the master MSP will send a I2C message with the device it would like to query and the query string, and the 2132 would switch the switches to route the UART to that device, send the query, get the reply, and send it back to the master MSP over I2C.
>
> Hope the intention is clearer now.
>
> Not sure what you mean by the 20 other I/O pins.
>
------------------------------------

______________________________
Stellaris® MCU Family: New Parts, New Package, New Price.


(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

What I'm actually saying is that perhaps you should review the whole
design. How many SPI devices are you using. How many I2C, what sort of
rate do these need to be accessed at. What sort of rate do the UART
devices need to be accessed at. It may well be that you are better off
allocating your hardware resources to the hardware UART rather than the
hardware SPI or I2C for example. OR ir may well be that you are better
off implementing a VERY simple UART using a timer on the 169 and EITHER
doing one UART and muxes, which takes a bit of management and overhead,
or doing it directly, if you have the I/O capacity, if you use a single
UART you can allocate a single timer A channel and use single duplex or
allocate 2 channels and go full duplex. You can do the same with Timer
B, except that timer B has only a single allocated pin per channel. You
can also allocate one capture pin per UART for receive mode and use the
same timer to time transmissions, without having to allocate a second
timer, but you then need to watch interrupt latency at higher baud
rates. Basically there are many wasy to resolve this issue, and I don't
think a second micro is up there as one of the best.

Al

merapcb wrote:
> --- In m...@yahoogroups.com, OneStone wrote:
>> I'm sorry but what you are saying makes absolutely no sense to me. Sure
>> I get what you have, a 169, running 1? SPI device and 1? I2C device, you
>> don't say how many, then you have 4 external devices with UARTS. Okay
>> I'd opt for a single 4052 anyway, its a dual 4:1, but that's a moot
>> point. Your cramming 4 channels into a shared pipe, which is okay, then
>> cramming them again down a single shared I2C pipe, which will require
>> quite a bit of overhead from the master anyway. this seems a less than
>> efficient way to do things. The first thing I'd do is get away from the
>> 169, but if you're stuck with it, and you shouldn't be if you're in the
>> hardware design stage, then sit and think carefully about the other
>> components, why the mix of SPI and I2C, is it necessary, how much
>> sharing is going on already on those lines? The 169 has a lot of I/o,
>> and a damned good Timer B that can single handedly implement 4 very nice
>> Uarts, although you might have to get a bit kludgy with the 4th, since
>> there are only 7 channels. I believe this will be far more efficient
>> than what you are planning, and less overhead for the micro.
>>
>> Al
>> OK, so you are saying mux/demux them in to a single software UART.... (at least I think that is what you are saying :-)
>
> Well no, actually you are saying implement 4 software UARTS, but hey if it's only one device *at a time* I need to talk with, I guess one software UART would do and mux/demux the Rx/Tx signals, right?
>
> OK it is finally sinking in.... if I can bit bang a single software UART, I can use your 4052.... (pity, I liked the 1:3 TS5A3359 I just found! ha)
>
> And yes, away from the 169.... far far away.... :-) But, not possible at the moment due to other dependencies. So that's why all of this. Else, I have my eye on a F5x or F24x with plenty of UARTs to go around...
> Thanks
> ------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Dave,
> If I need to "switch" logic paths to/from a set of external
> devices, why would I choose to use an analog like the
> 4051/4052/4053 family?
I don't recall anyone saying the slaves siganals were 0 - 3V in nature. What we know is they are UARTs, but not the voltage of the slaves. If there is a single TTL-232 transceiver, you'd need an analog switch capable of switching at least +12V and -12V. As I remember, the 405x family needs to be fed with a negative supply bigger in magnitude than the analog signal to be able to switch negative analog voltages, which I don't know if the OP is taking into accound.

Regards,
Michael K.

--- In m...@yahoogroups.com, "David Boyd" wrote:
>
> >
> > OK it is finally sinking in.... if I can bit bang a single software UART, I can use your 4052.... (pity, I liked the 1:3 TS5A3359 I just found! ha)
> > Regardless of all the other architectural options being thrown around, I'd like to make one point... perhaps in the form of a question to the more experienced folk on here.
>
> If I need to "switch" logic paths to/from a set of external devices, why would I choose to use an analog like the 4051/4052/4053 family? Wouldn't a set of data selectors/demuxes ('151, '153, '138, etc) be the purer design choice? I recall years ago, the FET analog switches were associated with latchup problems, ESD sensitivities, etc.
>
> Wouldn't you prefer logic gates to FET switches for logic steering?
>
> Dave
>
------------------------------------



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--- In m...@yahoogroups.com, "tintronic" wrote:
>

> I don't recall anyone saying the slaves siganals were 0 - 3V in nature. What we know is they are UARTs, but not the voltage of the slaves. If there is a single TTL-232 transceiver, you'd need an analog switch capable of switching at least +12V and -12V. As I remember, the 405x family needs to be fed with a negative supply bigger in magnitude than the analog signal to be able to switch negative analog voltages, which I don't know if the OP is taking into accound.
>
> Regards,
> Michael K.
>

I am the OP (phew...), so let me clarify again. There are three serial devices. Two of them are coming in via a 3232 (which gives us 3v TTL) and one is natively TTL also. So the muxing that is being talked about is not at the RS232 levels but at the 0-3v TTL levels. I hope this clarifies?

(and this is turning in to a very interesting discussion... at least for me, thank you everyone! Keep it coming)

------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

They are no longer the wimpy things they once were that fainted at the
sight of a finger. They come in automotive Hi-rel specs, 3.3V 5V
tolerant, CD74LVfamilies, HC, HCT etc. They are dirt cheap, and
bidirectional, perfect for this sort of app. There are even versions
around that take 3V control signals and can switch 40V signals.

Al
David Boyd wrote:
>> OK it is finally sinking in.... if I can bit bang a single software
>> UART, I can use your 4052.... (pity, I liked the 1:3 TS5A3359 I
>> just found! ha)
>> Regardless of all the other architectural options being thrown
> around, I'd like to make one point... perhaps in the form of a
> question to the more experienced folk on here.
>
> If I need to "switch" logic paths to/from a set of external devices,
> why would I choose to use an analog like the 4051/4052/4053 family?
> Wouldn't a set of data selectors/demuxes ('151, '153, '138, etc) be
> the purer design choice? I recall years ago, the FET analog switches
> were associated with latchup problems, ESD sensitivities, etc.
>
> Wouldn't you prefer logic gates to FET switches for logic steering?
>
> Dave
> ------------------------------------

______________________________
Stellaris® MCU Family: New Parts, New Package, New Price.


(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

On Mon, 17 Aug 2009 14:55:54 -0000, you wrote:

>OK so I am a dork, and I neglected to remember that you can't use both
> I2C on UART0 as well as the UART function.....
>
>I need to access (multiplex) a number of serial communication devices
> to the same (UART) port so plan on doing that with analog switches
> (and control lines for routing).
>
>So now what I am thinking, is to use an inexpensive MSP like 2132 as a
> I2C/UART bridge, meaning that the main MSP will query it over the
> I2C, the 2132 will route the query to the relevant peripheral over
> UART (and using the relevant analog switch configuration), and send
> back the reply to the master MSP.
>
>Sound like an OK design?
>
>Also, is it possible to take the master clock from the main MSP and
> this way save a crystal on the 2132?
>
>Thanks for your comments on this idea/design.....

I hope you will forgive my late arrival on this topic. A few years
ago, I had a similar problem (as I read it, anyway.) You can tell me
just how similar after I describe my earlier situation:

We had developed a completed system which included a single RS-232
port. But we later needed to hook up a bunch of them to a PC for data
logging and later analysis of the measurement samples from them. The
obvious idea was to consider some specialty RS-232 board for the IBM
PC, but at the time these were expensive and would require custom
software that would monitor all the ports and merge the data into a
single file. Another possible approach was to do what you are
suggesting above. But that would be yet another development project,
time was short, and we needed to set something up in a day or two --
not weeks. In the end, I thought for a little bit and suggested a
means by which we could hook up all the boards to a single RS-232 port
and co-mingle the outputs.

We had extra pins on the processors. Not many, and besides we didn't
want to have to do much 'wiring' to get this going. So I set up two
port pins on each board as 'grant' and 'address' as wire-or electrical
arrangements (using the PIC's ability to operate its own outputs as an
open-drain, if programmed that way.) We also wire-or'd the RS-232
drive/receive lines (the software on each board would only enable
their RS-232 pins [high impedance, otherwise] if and only if they were
granted access by the other two wires they shared.) We kept the
RS-232 electrical signal chips on all the boards (no mods other than
the wires to connect them) and just selected any one of the driver
chip pins to connect to the PC.

The software modification I made was trivial, really. And it took me
only a few hours to add. (Reprogramming the boards was easy.) Each
board's software had a unique (and short) coded binary address. Any
board ready to send output would first sample the grant line. If it
was already low, it held back and waited. If the grant line was
observed to be high, then the board would drive the grant line low and
then attempt to drive the address line bits on the address line. At
each bit time, it would either drive an active low (for a '0') or a
tristate high (for a '1'.) Then it would sample the address line. If
it matched what it thought it should be, it would drive out the next
address bit. If all the bits matched, it then decided that it owned
the RS-232, held the grant line, and operated the RS-232. Then
released the grant line.

Many times, as soon as a processor 'sees' the grant line high and
takes control by driving it low, all the other processors don't
interfere at all because when they see the grant line low they hold
off. So the one board seeking access just shifts out its address bits
with no competition. However, since the boards are running asynch
with each other, it's possible that two boards (or more) will both
observe the grant line 'high' around the same time and all decide to
drive the grant line low and start shifting out their address bits
near the same start time. (One must account for variations and this
is why such code cannot easily use C but must use assembly, so that
the cycle time for sample-to-grant-hold is known and precise, as well
as the bit shifting process that must take the same time regardless of
the bit time if you want the address-shift-out process to be faster.)
The design can be made entirely robust against variations between the
processors in their sampling time on grant and bit shifting. (Allow
enough time for each bit.) A processor driving an address 0 bit will
always observe a 0, obviously (don't need to look), so the processor
with the entire address of 0000, for example, will always "win" in
such a competition. However, there are '1' bits, then other
processors that also felt they might own the grant line may lose out.
When they drive a '1' and observe a '0', their software is set up to
then release both the address and grant lines to high impedance and
return to the wait-and-see condition before trying, once again.

It worked, superbly, and we could use any one of the working RS-232
outputs from any of the boards (as they were all driven exactly the
same, obviously.) Hardware mods were minimized (just a 4-wire ribbon
tapped to each board so that the RS-232 pair and the grant/address
pair were shared (Vcc logic levels only... the RS-232 chips and their
external RS-232 signaling level pins were left untouched.)

Jon
------------------------------------



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Hello,

Based on what you're writing and guessing a bit into your application, do you have both I2C devices as well as serial?

Let me outline your options:

1. You have both I2C and Serial (0-3TTL) devices:
-Solution: Based on the knowledge that you have a 169, you have both a UART and an I2C at your disposal. Use them both, and utilize a mux or two for Rx and Tx on your devices (I'm not a fan of wired-OR solutions, but this is your project here).

-Solution 2: Both interface modules are tied up for some reason, your original post is the next best solution.

2. You have JUST Serial (0-3TTL) devices:
-Solution: Mux it. I2C may have fewer lines for transmission on this, but muxing will be easier in the long run.

-Steve

________________________________
From: m...@yahoogroups.com [mailto:m...@yahoogroups.com] On Behalf Of merapcb
Sent: Monday, August 17, 2009 10:56 AM
To: m...@yahoogroups.com
Subject: [msp430] I2C / UART bridge?

OK so I am a dork, and I neglected to remember that you can't use both I2C on UART0 as well as the UART function.....

I need to access (multiplex) a number of serial communication devices to the same (UART) port so plan on doing that with analog switches (and control lines for routing).

So now what I am thinking, is to use an inexpensive MSP like 2132 as a I2C/UART bridge, meaning that the main MSP will query it over the I2C, the 2132 will route the query to the relevant peripheral over UART (and using the relevant analog switch configuration), and send back the reply to the master MSP.

Sound like an OK design?

Also, is it possible to take the master clock from the main MSP and this way save a crystal on the 2132?

Thanks for your comments on this idea/design.....

[Non-text portions of this message have been removed]

------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

> There are three serial devices. Two of them are coming in via a
> 3232 (which gives us 3v TTL) and one is natively TTL also.

So, for mixing the 3 UARTs into one:
1) You don't need an analog mux, a digital mux or switches (like the 4066) will suffice. Even 3 OR gates will do it (inputs are MSP-TX and #SELx signal, outputs go to the 3 slaves RX signals).
2) You can use a 3-input AND gate (or two 2-input AND gates) for mixing the slave TX lines into the MSP RX line.

We still don't know what your I2C and SPI devices are.

Regards,
Michael K.

--- In m...@yahoogroups.com, "merapcb" wrote:
>
> --- In m...@yahoogroups.com, "tintronic" wrote:
> > > I don't recall anyone saying the slaves siganals were 0 - 3V in nature. What we know is they are UARTs, but not the voltage of the slaves. If there is a single TTL-232 transceiver, you'd need an analog switch capable of switching at least +12V and -12V. As I remember, the 405x family needs to be fed with a negative supply bigger in magnitude than the analog signal to be able to switch negative analog voltages, which I don't know if the OP is taking into accound.
> >
> > Regards,
> > Michael K.
> > I am the OP (phew...), so let me clarify again. There are three serial devices. Two of them are coming in via a 3232 (which gives us 3v TTL) and one is natively TTL also. So the muxing that is being talked about is not at the RS232 levels but at the 0-3v TTL levels. I hope this clarifies?
>
> (and this is turning in to a very interesting discussion... at least for me, thank you everyone! Keep it coming)
>
------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

You mention that < queried. So that makes them half duplex.>> So can you control the
transmit (output) lines on the remote devices? If so make them
tri-state (float them) and then you don't need any muxes. Just
connect them all together to the '169 i/o pin for a multi-drop link
and only heave the individual slave enable it's transmit output when
responding to a query. Down side is if a remote slave failure occurs
it can kill the bus.
Hugh

At 01:26 PM 8/17/2009, you wrote:
> > There are three serial devices. Two of them are coming in via a
> > 3232 (which gives us 3v TTL) and one is natively TTL also.
>
>So, for mixing the 3 UARTs into one:
>1) You don't need an analog mux, a digital mux or switches (like the
>4066) will suffice. Even 3 OR gates will do it (inputs are MSP-TX
>and #SELx signal, outputs go to the 3 slaves RX signals).
>2) You can use a 3-input AND gate (or two 2-input AND gates) for
>mixing the slave TX lines into the MSP RX line.
>
>We still don't know what your I2C and SPI devices are.
>
>Regards,
>Michael K.
>
>--- In m...@yahoogroups.com, "merapcb" wrote:
> >
> > --- In m...@yahoogroups.com, "tintronic" wrote:
> > >
> >
> > > I don't recall anyone saying the slaves siganals were 0 - 3V in
> nature. What we know is they are UARTs, but not the voltage of the
> slaves. If there is a single TTL-232 transceiver, you'd need an
> analog switch capable of switching at least +12V and -12V. As I
> remember, the 405x family needs to be fed with a negative supply
> bigger in magnitude than the analog signal to be able to switch
> negative analog voltages, which I don't know if the OP is taking into accound.
> > >
> > > Regards,
> > > Michael K.
> > >
> >
> > I am the OP (phew...), so let me clarify again. There are three
> serial devices. Two of them are coming in via a 3232 (which gives
> us 3v TTL) and one is natively TTL also. So the muxing that is
> being talked about is not at the RS232 levels but at the 0-3v TTL
> levels. I hope this clarifies?
> >
> > (and this is turning in to a very interesting discussion... at
> least for me, thank you everyone! Keep it coming)
> >
>------------------------------------

______________________________
Stellaris® MCU Family: New Parts, New Package, New Price.


(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Folks,

Thanks to all for the various ideas and insights about this issue.
After deliberation it was decided to use UART0 (by re configuring from I2C when needed and then back to I2C). MUX can be done with 4052 as Al suggested. Thank you Al.

I have posted the schematic of the proposed solution here:
http://tinyurl.com/lmn8k5

Comments are most welcome, I have not used this before so I hope I got it right.

Also, by the way, what is the best way of protecting the external RS232 lines from unwanted (accidental) voltages getting connected? (automotive environment). Diodes? Series resistors?

Thanks

PS - Pay attention to he nifty way of being able to connect more than one device to the same port (not at the same time) and having it sensed (well, nifty I think so)
------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

You're welcome, the link doesn't work for me. When I used to design for
automotive I generally used a series resistor and an SCR clamp like an
SP720 (which I think is now discontinued) or the SP724. These could
handle typical automotive load dumps, unlike some other possible
solutions which were not designed to deal with such high energy loads.
They are available from Littlefuse. The SP724 is a quad array.

Al

merapcb wrote:
> Folks,
>
> Thanks to all for the various ideas and insights about this issue.
> After deliberation it was decided to use UART0 (by re configuring from I2C when needed and then back to I2C). MUX can be done with 4052 as Al suggested. Thank you Al.
>
> I have posted the schematic of the proposed solution here:
> http://tinyurl.com/lmn8k5
>
> Comments are most welcome, I have not used this before so I hope I got it right.
>
> Also, by the way, what is the best way of protecting the external RS232 lines from unwanted (accidental) voltages getting connected? (automotive environment). Diodes? Series resistors?
>
> Thanks
>
> PS - Pay attention to he nifty way of being able to connect more than one device to the same port (not at the same time) and having it sensed (well, nifty I think so)
> ------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

--- In m...@yahoogroups.com, OneStone wrote:
>
> You're welcome, the link doesn't work for me. =

Here it is, it is actually uploaded in the file section here under "Uploads"

http://f1.grp.yahoofs.com/v1/kE6LSooh9eUwIoNdW5n1aHHJ8S-eYASwduV96MWE3H2Yc57D0ad1Ku50fD_VrM1suVfU0YQBwPn9URqat5B9VZLk-yux/Uploads/UART%20MUX%20with%204052.png

Hope this works
------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

The link doesn't work but the schematic is easy to find with the
provided directions.

Howard

merapcb wrote:
>
>
> --- In m...@yahoogroups.com ,
> OneStone wrote:
> >
> > You're welcome, the link doesn't work for me. =
>
> Here it is, it is actually uploaded in the file section here under
> "Uploads"
>
> http://f1.grp.yahoofs.com/v1/kE6LSooh9eUwIoNdW5n1aHHJ8S-eYASwduV96MWE3H2Yc57D0ad1Ku50fD_VrM1suVfU0YQBwPn9URqat5B9VZLk-yux/Uploads/UART%20MUX%20with%204052.png
> Hope this works

------------------------------------



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NOPE 'DOCUMENT NOT FOUND'

AL

merapcb wrote:
> --- In m...@yahoogroups.com, OneStone wrote:
>> You're welcome, the link doesn't work for me. =
>
> Here it is, it is actually uploaded in the file section here under "Uploads"
>
> http://f1.grp.yahoofs.com/v1/kE6LSooh9eUwIoNdW5n1aHHJ8S-eYASwduV96MWE3H2Yc57D0ad1Ku50fD_VrM1suVfU0YQBwPn9URqat5B9VZLk-yux/Uploads/UART%20MUX%20with%204052.png
>
> Hope this works
> ------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

--- In m...@yahoogroups.com, OneStone wrote:
>
> NOPE 'DOCUMENT NOT FOUND'
>
> AL
>

Oh my..... but if I go to "Files > Uploads" on this forum then I do see it. Is there something I don't know about the file system here? Maybe it is not public? :-(
------------------------------------

______________________________
Stellaris® MCU Family: New Parts, New Package, New Price.


(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

The problem is sometimes Yahoo provides a temporary link to a file and
as soon as you log off the link is broken. Whereas a link like the
following is permanent.
http://tech.groups.yahoo.com/group/msp430/files/Uploads/
Be suspicious of any link to a file with more than 80 characters in the
link Yahoo provides.

Howard
merapcb wrote:
>
>
> --- In m...@yahoogroups.com ,
> OneStone wrote:
> >
> > NOPE 'DOCUMENT NOT FOUND'
> >
> > AL
> > Oh my..... but if I go to "Files > Uploads" on this forum then I do
> see it. Is there something I don't know about the file system here?
> Maybe it is not public? :-(

------------------------------------



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Al,
> When I used to design for automotive I generally used a series
> resistor and an SCR clamp like an SP720 (...)

Surely you meant a TVS (Transient Voltage Supressor) instead of SCR
(Silicon Controlled Rectifier), right?

merapcb,
> > Also, by the way, what is the best way of protecting the external
> > RS232 lines from unwanted (accidental) voltages getting
> > connected?

I guess, like assumed by Al, you don't mean to protect the device against a wrong connection but against voltage spikes.

I agree that series resistor and TVS bypass should be an adequate solution. I'd add ferrite beads in series too.

Regards,
Michael K.

--- In m...@yahoogroups.com, OneStone wrote:
>
> You're welcome, the link doesn't work for me. When I used to design for
> automotive I generally used a series resistor and an SCR clamp like an
> SP720 (which I think is now discontinued) or the SP724. These could
> handle typical automotive load dumps, unlike some other possible
> solutions which were not designed to deal with such high energy loads.
> They are available from Littlefuse. The SP724 is a quad array.
>
> Al
>
> merapcb wrote:
> > Folks,
> >
> > Thanks to all for the various ideas and insights about this issue.
> > After deliberation it was decided to use UART0 (by re configuring from I2C when needed and then back to I2C). MUX can be done with 4052 as Al suggested. Thank you Al.
> >
> > I have posted the schematic of the proposed solution here:
> > http://tinyurl.com/lmn8k5
> >
> > Comments are most welcome, I have not used this before so I hope I got it right.
> >
> > Also, by the way, what is the best way of protecting the external RS232 lines from unwanted (accidental) voltages getting connected? (automotive environment). Diodes? Series resistors?
> >
> > Thanks
> >
> > PS - Pay attention to he nifty way of being able to connect more than one device to the same port (not at the same time) and having it sensed (well, nifty I think so)
> >
> >
> >
> >
> > ------------------------------------
> >
> >
> >
> >



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Read the spec for the SP724, you will find that each circuit is a
combination of SCR's resistors and a diode. Whereas a transient voltage
suppressor is actually a diode, or diode pair, and may be
uni-directional or bidirectional.

"The SP724 is a quad array of transient voltage clamping circuits
designed to suppress ESD and other transient over-voltage events. The
SP724 is used to help protect sensitive digital or analog input circuits
on data, signal, or control lines operating on power supplies up to 20VDC.

The SP724 is comprised of bipolar SCR/diode structures to protect up to
four independent lines by clamping transients of either polarity to the
power supply rails. The SP724 offers very low leakage (1nA Typical) and
low input capacitance (3pF Typical). Additionally, the SP724 is rated to
withstand the IEC 61000-4-2 ESD specification for both contact and air
discharge methods to level 4.

The SP724 is connected to the sensitive input line and its associated
power supply lines. Clamping action occurs during the transient pulse,
turning on the diode and fast triggering SCR structures when the voltage
on the input line exceeds one VBE threshold above the V+ supply (or one
VBE threshold below the V- supply). Therefore, the SP724 operation is
unaffected by poor power supply regulation or voltage fluctuations
within its operating range."

Cheers

Al
tintronic wrote:
> Al,
>> When I used to design for automotive I generally used a series
>> resistor and an SCR clamp like an SP720 (...)
>
> Surely you meant a TVS (Transient Voltage Supressor) instead of SCR
> (Silicon Controlled Rectifier), right?
>
> merapcb,
>>> Also, by the way, what is the best way of protecting the external
>>> RS232 lines from unwanted (accidental) voltages getting
>>> connected?
>
> I guess, like assumed by Al, you don't mean to protect the device against a wrong connection but against voltage spikes.
>
> I agree that series resistor and TVS bypass should be an adequate solution. I'd add ferrite beads in series too.
>
> Regards,
> Michael K.
>
> --- In m...@yahoogroups.com, OneStone wrote:
>> You're welcome, the link doesn't work for me. When I used to design for
>> automotive I generally used a series resistor and an SCR clamp like an
>> SP720 (which I think is now discontinued) or the SP724. These could
>> handle typical automotive load dumps, unlike some other possible
>> solutions which were not designed to deal with such high energy loads.
>> They are available from Littlefuse. The SP724 is a quad array.
>>
>> Al
>>
>> merapcb wrote:
>>> Folks,
>>>
>>> Thanks to all for the various ideas and insights about this issue.
>>> After deliberation it was decided to use UART0 (by re configuring from I2C when needed and then back to I2C). MUX can be done with 4052 as Al suggested. Thank you Al.
>>>
>>> I have posted the schematic of the proposed solution here:
>>> http://tinyurl.com/lmn8k5
>>>
>>> Comments are most welcome, I have not used this before so I hope I got it right.
>>>
>>> Also, by the way, what is the best way of protecting the external RS232 lines from unwanted (accidental) voltages getting connected? (automotive environment). Diodes? Series resistors?
>>>
>>> Thanks
>>>
>>> PS - Pay attention to he nifty way of being able to connect more than one device to the same port (not at the same time) and having it sensed (well, nifty I think so)
>>>
>>>
>>>
>>>
>>> ------------------------------------
>>>
>>>
>>>
>>>



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Al,
When I saw the word SCR, my first thought was "that's an interesting idea, that would allow the protection to absorb more current than the TVS solution I use, but then it would stay clamped unitll power is recycled". I finished reading the post and searched for the datasheet. In fact it is till open an the 4th tab prior to this one on my web browser. The way I saw it, the SP724 is a TVS. That is its function and purpose. The fact that it internally uses SCRs as opposed to zener or shotkky diodes or other techniques doesn't correctly classify it, in my opinion, as an SCR, but rather a TVS. Or am I wrong and the SP724 is an automotive solution that took the previously used arrays of single SCRs into a single chip, turning it into a TVS?

That was my opinion and why I asked you if you meant TVS or in fact you meant SCR. I guess that depends on what you were looking for when you desided for the SP72x. Were you looking for an SCR array or were you looking for a high current TVS?

My intention in writing the post was more to guide the OP, having him searching on the TVS concept and solutions instead of SCRs, if that was what you in fact meant, which is why I wrote it as a question. I also quoted what I understood by SCR, because it might just as well have standed for a different concept than Silicon Controlled Rectifier, althought on a quick search throught google and wikipedia I hadn't found any other electonic related concept abreviated by SCR.
> > Al,
> > > When I used to design for automotive I generally used a series
> > > resistor and an SCR clamp like an SP720 (...)
> > Surely you meant a TVS (Transient Voltage Supressor) instead of
> > SCR (Silicon Controlled Rectifier), right?

Your quoting of the datasheet doesn't clarify this for me,so I would very much appreciate to know (if you remember, as it might well be that this is part of your backround knowledge), if you were looking for an SCR array or a high current TVS (or something else) when you came across the SP72x.

Best Regards,
Michael K.

--- In m...@yahoogroups.com, OneStone wrote:
>
> Read the spec for the SP724, you will find that each circuit is a
> combination of SCR's resistors and a diode. Whereas a transient voltage
> suppressor is actually a diode, or diode pair, and may be
> uni-directional or bidirectional.
>
> "The SP724 is a quad array of transient voltage clamping circuits
> designed to suppress ESD and other transient over-voltage events. The
> SP724 is used to help protect sensitive digital or analog input circuits
> on data, signal, or control lines operating on power supplies up to 20VDC.
>
> The SP724 is comprised of bipolar SCR/diode structures to protect up to
> four independent lines by clamping transients of either polarity to the
> power supply rails. The SP724 offers very low leakage (1nA Typical) and
> low input capacitance (3pF Typical). Additionally, the SP724 is rated to
> withstand the IEC 61000-4-2 ESD specification for both contact and air
> discharge methods to level 4.
>
> The SP724 is connected to the sensitive input line and its associated
> power supply lines. Clamping action occurs during the transient pulse,
> turning on the diode and fast triggering SCR structures when the voltage
> on the input line exceeds one VBE threshold above the V+ supply (or one
> VBE threshold below the V- supply). Therefore, the SP724 operation is
> unaffected by poor power supply regulation or voltage fluctuations
> within its operating range."
>
> Cheers
>
> Al
> tintronic wrote:
> > Al,
> >> When I used to design for automotive I generally used a series
> >> resistor and an SCR clamp like an SP720 (...)
> >
> > Surely you meant a TVS (Transient Voltage Supressor) instead of SCR
> > (Silicon Controlled Rectifier), right?
> >
> > merapcb,
> >>> Also, by the way, what is the best way of protecting the external
> >>> RS232 lines from unwanted (accidental) voltages getting
> >>> connected?
> >
> > I guess, like assumed by Al, you don't mean to protect the device against a wrong connection but against voltage spikes.
> >
> > I agree that series resistor and TVS bypass should be an adequate solution. I'd add ferrite beads in series too.
> >
> > Regards,
> > Michael K.
> >
> > --- In m...@yahoogroups.com, OneStone wrote:
> >> You're welcome, the link doesn't work for me. When I used to design for
> >> automotive I generally used a series resistor and an SCR clamp like an
> >> SP720 (which I think is now discontinued) or the SP724. These could
> >> handle typical automotive load dumps, unlike some other possible
> >> solutions which were not designed to deal with such high energy loads.
> >> They are available from Littlefuse. The SP724 is a quad array.
> >>
> >> Al
> >>
> >> merapcb wrote:
> >>> Folks,
> >>>
> >>> Thanks to all for the various ideas and insights about this issue.
> >>> After deliberation it was decided to use UART0 (by re configuring from I2C when needed and then back to I2C). MUX can be done with 4052 as Al suggested. Thank you Al.
> >>>
> >>> I have posted the schematic of the proposed solution here:
> >>> http://tinyurl.com/lmn8k5
> >>>
> >>> Comments are most welcome, I have not used this before so I hope I got it right.
> >>>
> >>> Also, by the way, what is the best way of protecting the external RS232 lines from unwanted (accidental) voltages getting connected? (automotive environment). Diodes? Series resistors?
> >>>
> >>> Thanks
> >>>
> >>> PS - Pay attention to he nifty way of being able to connect more than one device to the same port (not at the same time) and having it sensed (well, nifty I think so)
> >>>
> >>>
> >>>
> >>>
> >>> ------------------------------------
> >>>
> >>>
> >>>
> >>>



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Hi Michael. I specifically selected the SP724 because it has an SCR as
its core. I have designed many ECU's in the past most using the SP724's
big brother, the SP720, which became discontinued when Harris (the
original manufacturer) shut down, and passed the baton to Intersil, who
later passed it again to Littlefuse. I still have a couple of hundred
SP720s in boxes somewhere. I never lost an input or an output line to
one, despite some really nasty stuff, like fires, major load dumps, 42V
connects to signal lines, even some idiot connecting a coil to one. In
my opinion they are a better option for heavy duty automotive work than
anything else I've found.

Al

tintronic wrote:
> Al,
> When I saw the word SCR, my first thought was "that's an interesting idea, that would allow the protection to absorb more current than the TVS solution I use, but then it would stay clamped unitll power is recycled". I finished reading the post and searched for the datasheet. In fact it is till open an the 4th tab prior to this one on my web browser. The way I saw it, the SP724 is a TVS. That is its function and purpose. The fact that it internally uses SCRs as opposed to zener or shotkky diodes or other techniques doesn't correctly classify it, in my opinion, as an SCR, but rather a TVS. Or am I wrong and the SP724 is an automotive solution that took the previously used arrays of single SCRs into a single chip, turning it into a TVS?
>
> That was my opinion and why I asked you if you meant TVS or in fact you meant SCR. I guess that depends on what you were looking for when you desided for the SP72x. Were you looking for an SCR array or were you looking for a high current TVS?
>
> My intention in writing the post was more to guide the OP, having him searching on the TVS concept and solutions instead of SCRs, if that was what you in fact meant, which is why I wrote it as a question. I also quoted what I understood by SCR, because it might just as well have standed for a different concept than Silicon Controlled Rectifier, althought on a quick search throught google and wikipedia I hadn't found any other electonic related concept abreviated by SCR.
>>> Al,
>>>> When I used to design for automotive I generally used a series
>>>> resistor and an SCR clamp like an SP720 (...)
>>> Surely you meant a TVS (Transient Voltage Supressor) instead of
>>> SCR (Silicon Controlled Rectifier), right?
>
> Your quoting of the datasheet doesn't clarify this for me,so I would very much appreciate to know (if you remember, as it might well be that this is part of your backround knowledge), if you were looking for an SCR array or a high current TVS (or something else) when you came across the SP72x.
>
> Best Regards,
> Michael K.
>
> --- In m...@yahoogroups.com, OneStone wrote:
>> Read the spec for the SP724, you will find that each circuit is a
>> combination of SCR's resistors and a diode. Whereas a transient voltage
>> suppressor is actually a diode, or diode pair, and may be
>> uni-directional or bidirectional.
>>
>> "The SP724 is a quad array of transient voltage clamping circuits
>> designed to suppress ESD and other transient over-voltage events. The
>> SP724 is used to help protect sensitive digital or analog input circuits
>> on data, signal, or control lines operating on power supplies up to 20VDC.
>>
>> The SP724 is comprised of bipolar SCR/diode structures to protect up to
>> four independent lines by clamping transients of either polarity to the
>> power supply rails. The SP724 offers very low leakage (1nA Typical) and
>> low input capacitance (3pF Typical). Additionally, the SP724 is rated to
>> withstand the IEC 61000-4-2 ESD specification for both contact and air
>> discharge methods to level 4.
>>
>> The SP724 is connected to the sensitive input line and its associated
>> power supply lines. Clamping action occurs during the transient pulse,
>> turning on the diode and fast triggering SCR structures when the voltage
>> on the input line exceeds one VBE threshold above the V+ supply (or one
>> VBE threshold below the V- supply). Therefore, the SP724 operation is
>> unaffected by poor power supply regulation or voltage fluctuations
>> within its operating range."
>>
>> Cheers
>>
>> Al
>> tintronic wrote:
>>> Al,
>>>> When I used to design for automotive I generally used a series
>>>> resistor and an SCR clamp like an SP720 (...)
>>> Surely you meant a TVS (Transient Voltage Supressor) instead of SCR
>>> (Silicon Controlled Rectifier), right?
>>>
>>> merapcb,
>>>>> Also, by the way, what is the best way of protecting the external
>>>>> RS232 lines from unwanted (accidental) voltages getting
>>>>> connected?
>>> I guess, like assumed by Al, you don't mean to protect the device against a wrong connection but against voltage spikes.
>>>
>>> I agree that series resistor and TVS bypass should be an adequate solution. I'd add ferrite beads in series too.
>>>
>>> Regards,
>>> Michael K.
>>>
>>> --- In m...@yahoogroups.com, OneStone wrote:
>>>> You're welcome, the link doesn't work for me. When I used to design for
>>>> automotive I generally used a series resistor and an SCR clamp like an
>>>> SP720 (which I think is now discontinued) or the SP724. These could
>>>> handle typical automotive load dumps, unlike some other possible
>>>> solutions which were not designed to deal with such high energy loads.
>>>> They are available from Littlefuse. The SP724 is a quad array.
>>>>
>>>> Al
>>>>
>>>> merapcb wrote:
>>>>> Folks,
>>>>>
>>>>> Thanks to all for the various ideas and insights about this issue.
>>>>> After deliberation it was decided to use UART0 (by re configuring from I2C when needed and then back to I2C). MUX can be done with 4052 as Al suggested. Thank you Al.
>>>>>
>>>>> I have posted the schematic of the proposed solution here:
>>>>> http://tinyurl.com/lmn8k5
>>>>>
>>>>> Comments are most welcome, I have not used this before so I hope I got it right.
>>>>>
>>>>> Also, by the way, what is the best way of protecting the external RS232 lines from unwanted (accidental) voltages getting connected? (automotive environment). Diodes? Series resistors?
>>>>>
>>>>> Thanks
>>>>>
>>>>> PS - Pay attention to he nifty way of being able to connect more than one device to the same port (not at the same time) and having it sensed (well, nifty I think so)
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ------------------------------------
>>>>>
>>>>>
>>>>>
>>>>>



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Al,

If I might digress on this, since you mentioned ECUs and stuff...

I am in fact designing something automotive, and am concerned about port protection.

The serial ports I mentioned in my OP plug in to our own equipment, not the vehicle, so in theory I am not too much worried about them, only about someone actually intentionally or by mistake either short circuiting the pins or the likes.

Regarding digital IO lines, presently I am using a simple dual schotcky configuration (two 5819's) with a R/C in front (but am thinking of replacing them with BAV99s). While listening to you advocate the SP724, I am wondering whether my method of protection is not adequate enough?

By the way, my power section is based on a good old LM2575 for 5v and a LDO for 3.3 (dual rails) and no particular protection other than a diode on the input for reverse polarity. Touch wood so far I have had these on truck without any issue, but would you recommend looking at a TVS component/circuit also?

Thanks

PS - Sorry guys if this is too OT!
--- In m...@yahoogroups.com, OneStone wrote:
>
> Hi Michael. I specifically selected the SP724 because it has an SCR as
> its core. I have designed many ECU's in the past most using the SP724's
> big brother, the SP720, which became discontinued when Harris (the
> original manufacturer) shut down, and passed the baton to Intersil, who
> later passed it again to Littlefuse. I still have a couple of hundred
> SP720s in boxes somewhere. I never lost an input or an output line to
> one, despite some really nasty stuff, like fires, major load dumps, 42V
> connects to signal lines, even some idiot connecting a coil to one. In
> my opinion they are a better option for heavy duty automotive work than
> anything else I've found.
>
> Al
>
> tintronic wrote:
> > Al,
> > When I saw the word SCR, my first thought was "that's an interesting idea, that would allow the protection to absorb more current than the TVS solution I use, but then it would stay clamped unitll power is recycled". I finished reading the post and searched for the datasheet. In fact it is till open an the 4th tab prior to this one on my web browser. The way I saw it, the SP724 is a TVS. That is its function and purpose. The fact that it internally uses SCRs as opposed to zener or shotkky diodes or other techniques doesn't correctly classify it, in my opinion, as an SCR, but rather a TVS. Or am I wrong and the SP724 is an automotive solution that took the previously used arrays of single SCRs into a single chip, turning it into a TVS?
> >
> > That was my opinion and why I asked you if you meant TVS or in fact you meant SCR. I guess that depends on what you were looking for when you desided for the SP72x. Were you looking for an SCR array or were you looking for a high current TVS?
> >
> > My intention in writing the post was more to guide the OP, having him searching on the TVS concept and solutions instead of SCRs, if that was what you in fact meant, which is why I wrote it as a question. I also quoted what I understood by SCR, because it might just as well have standed for a different concept than Silicon Controlled Rectifier, althought on a quick search throught google and wikipedia I hadn't found any other electonic related concept abreviated by SCR.
> >>> Al,
> >>>> When I used to design for automotive I generally used a series
> >>>> resistor and an SCR clamp like an SP720 (...)
> >>> Surely you meant a TVS (Transient Voltage Supressor) instead of
> >>> SCR (Silicon Controlled Rectifier), right?
> >
> > Your quoting of the datasheet doesn't clarify this for me,so I would very much appreciate to know (if you remember, as it might well be that this is part of your backround knowledge), if you were looking for an SCR array or a high current TVS (or something else) when you came across the SP72x.
> >
> > Best Regards,
> > Michael K.
> >
> > --- In m...@yahoogroups.com, OneStone wrote:
> >> Read the spec for the SP724, you will find that each circuit is a
> >> combination of SCR's resistors and a diode. Whereas a transient voltage
> >> suppressor is actually a diode, or diode pair, and may be
> >> uni-directional or bidirectional.
> >>
> >> "The SP724 is a quad array of transient voltage clamping circuits
> >> designed to suppress ESD and other transient over-voltage events. The
> >> SP724 is used to help protect sensitive digital or analog input circuits
> >> on data, signal, or control lines operating on power supplies up to 20VDC.
> >>
> >> The SP724 is comprised of bipolar SCR/diode structures to protect up to
> >> four independent lines by clamping transients of either polarity to the
> >> power supply rails. The SP724 offers very low leakage (1nA Typical) and
> >> low input capacitance (3pF Typical). Additionally, the SP724 is rated to
> >> withstand the IEC 61000-4-2 ESD specification for both contact and air
> >> discharge methods to level 4.
> >>
> >> The SP724 is connected to the sensitive input line and its associated
> >> power supply lines. Clamping action occurs during the transient pulse,
> >> turning on the diode and fast triggering SCR structures when the voltage
> >> on the input line exceeds one VBE threshold above the V+ supply (or one
> >> VBE threshold below the V- supply). Therefore, the SP724 operation is
> >> unaffected by poor power supply regulation or voltage fluctuations
> >> within its operating range."
> >>
> >> Cheers
> >>
> >> Al
> >>
> >>
> >> tintronic wrote:
> >>> Al,
> >>>> When I used to design for automotive I generally used a series
> >>>> resistor and an SCR clamp like an SP720 (...)
> >>> Surely you meant a TVS (Transient Voltage Supressor) instead of SCR
> >>> (Silicon Controlled Rectifier), right?
> >>>
> >>> merapcb,
> >>>>> Also, by the way, what is the best way of protecting the external
> >>>>> RS232 lines from unwanted (accidental) voltages getting
> >>>>> connected?
> >>> I guess, like assumed by Al, you don't mean to protect the device against a wrong connection but against voltage spikes.
> >>>
> >>> I agree that series resistor and TVS bypass should be an adequate solution. I'd add ferrite beads in series too.
> >>>
> >>> Regards,
> >>> Michael K.
> >>>
> >>> --- In m...@yahoogroups.com, OneStone wrote:
> >>>> You're welcome, the link doesn't work for me. When I used to design for
> >>>> automotive I generally used a series resistor and an SCR clamp like an
> >>>> SP720 (which I think is now discontinued) or the SP724. These could
> >>>> handle typical automotive load dumps, unlike some other possible
> >>>> solutions which were not designed to deal with such high energy loads.
> >>>> They are available from Littlefuse. The SP724 is a quad array.
> >>>>
> >>>> Al
> >>>>
> >>>> merapcb wrote:
> >>>>> Folks,
> >>>>>
> >>>>> Thanks to all for the various ideas and insights about this issue.
> >>>>> After deliberation it was decided to use UART0 (by re configuring from I2C when needed and then back to I2C). MUX can be done with 4052 as Al suggested. Thank you Al.
> >>>>>
> >>>>> I have posted the schematic of the proposed solution here:
> >>>>> http://tinyurl.com/lmn8k5
> >>>>>
> >>>>> Comments are most welcome, I have not used this before so I hope I got it right.
> >>>>>
> >>>>> Also, by the way, what is the best way of protecting the external RS232 lines from unwanted (accidental) voltages getting connected? (automotive environment). Diodes? Series resistors?
> >>>>>
> >>>>> Thanks
> >>>>>
> >>>>> PS - Pay attention to he nifty way of being able to connect more than one device to the same port (not at the same time) and having it sensed (well, nifty I think so)
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>> ------------------------------------
> >>>>>
> >>>>>
> >>>>>
> >>>>>



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Years ago I tried BAV99's, but in tests back in 1994 I discovered that
these simply couldn't handle an automotive load dump. Another problem I
faced at that time was the HCMOS micros from Moto. HCMOS was/is very
prone to latch up if it saw anything that exceeded pwr/gnd by 0.3V, and
small negative swings seemed particularly damaging. After a lot of
testing I arrived at the SP720, and have stayed with it since. My power
supply of choice in those days was typically a LOT more robust that
yours appears to be, a simple regulator will not stop large fast
transients. My later designs for the MSP430 had the following set up:-

blocking diode - smallish 1W series resistor TVS (SP724 for I/O only),
100n cap, 100uH 2A inductor, 100n cap 47uF 25V cap, PQ20VZ11 switcher
for 5V same for 3V3, both followed by 47UF 10V and 100n caps then pi
filters.

That one was designed in 2000 using a 149 to drive 8 injectors and 8
ignition coils, it was credit card sized, in a 3 card stack, and had an
RFM TR1000 RF link that allowed remote data read and tuning real time.

Al

merapcb wrote:
> Al,
>
> If I might digress on this, since you mentioned ECUs and stuff...
>
> I am in fact designing something automotive, and am concerned about port protection.
>
> The serial ports I mentioned in my OP plug in to our own equipment, not the vehicle, so in theory I am not too much worried about them, only about someone actually intentionally or by mistake either short circuiting the pins or the likes.
>
> Regarding digital IO lines, presently I am using a simple dual schotcky configuration (two 5819's) with a R/C in front (but am thinking of replacing them with BAV99s). While listening to you advocate the SP724, I am wondering whether my method of protection is not adequate enough?
>
> By the way, my power section is based on a good old LM2575 for 5v and a LDO for 3.3 (dual rails) and no particular protection other than a diode on the input for reverse polarity. Touch wood so far I have had these on truck without any issue, but would you recommend looking at a TVS component/circuit also?
>
> Thanks
>
> PS - Sorry guys if this is too OT!
> --- In m...@yahoogroups.com, OneStone wrote:
>> Hi Michael. I specifically selected the SP724 because it has an SCR as
>> its core. I have designed many ECU's in the past most using the SP724's
>> big brother, the SP720, which became discontinued when Harris (the
>> original manufacturer) shut down, and passed the baton to Intersil, who
>> later passed it again to Littlefuse. I still have a couple of hundred
>> SP720s in boxes somewhere. I never lost an input or an output line to
>> one, despite some really nasty stuff, like fires, major load dumps, 42V
>> connects to signal lines, even some idiot connecting a coil to one. In
>> my opinion they are a better option for heavy duty automotive work than
>> anything else I've found.
>>
>> Al
>>
>> tintronic wrote:
>>> Al,
>>> When I saw the word SCR, my first thought was "that's an interesting idea, that would allow the protection to absorb more current than the TVS solution I use, but then it would stay clamped unitll power is recycled". I finished reading the post and searched for the datasheet. In fact it is till open an the 4th tab prior to this one on my web browser. The way I saw it, the SP724 is a TVS. That is its function and purpose. The fact that it internally uses SCRs as opposed to zener or shotkky diodes or other techniques doesn't correctly classify it, in my opinion, as an SCR, but rather a TVS. Or am I wrong and the SP724 is an automotive solution that took the previously used arrays of single SCRs into a single chip, turning it into a TVS?
>>>
>>> That was my opinion and why I asked you if you meant TVS or in fact you meant SCR. I guess that depends on what you were looking for when you desided for the SP72x. Were you looking for an SCR array or were you looking for a high current TVS?
>>>
>>> My intention in writing the post was more to guide the OP, having him searching on the TVS concept and solutions instead of SCRs, if that was what you in fact meant, which is why I wrote it as a question. I also quoted what I understood by SCR, because it might just as well have standed for a different concept than Silicon Controlled Rectifier, althought on a quick search throught google and wikipedia I hadn't found any other electonic related concept abreviated by SCR.
>>>>> Al,
>>>>>> When I used to design for automotive I generally used a series
>>>>>> resistor and an SCR clamp like an SP720 (...)
>>>>> Surely you meant a TVS (Transient Voltage Supressor) instead of
>>>>> SCR (Silicon Controlled Rectifier), right?
>>> Your quoting of the datasheet doesn't clarify this for me,so I would very much appreciate to know (if you remember, as it might well be that this is part of your backround knowledge), if you were looking for an SCR array or a high current TVS (or something else) when you came across the SP72x.
>>>
>>> Best Regards,
>>> Michael K.
>>>
>>> --- In m...@yahoogroups.com, OneStone wrote:
>>>> Read the spec for the SP724, you will find that each circuit is a
>>>> combination of SCR's resistors and a diode. Whereas a transient voltage
>>>> suppressor is actually a diode, or diode pair, and may be
>>>> uni-directional or bidirectional.
>>>>
>>>> "The SP724 is a quad array of transient voltage clamping circuits
>>>> designed to suppress ESD and other transient over-voltage events. The
>>>> SP724 is used to help protect sensitive digital or analog input circuits
>>>> on data, signal, or control lines operating on power supplies up to 20VDC.
>>>>
>>>> The SP724 is comprised of bipolar SCR/diode structures to protect up to
>>>> four independent lines by clamping transients of either polarity to the
>>>> power supply rails. The SP724 offers very low leakage (1nA Typical) and
>>>> low input capacitance (3pF Typical). Additionally, the SP724 is rated to
>>>> withstand the IEC 61000-4-2 ESD specification for both contact and air
>>>> discharge methods to level 4.
>>>>
>>>> The SP724 is connected to the sensitive input line and its associated
>>>> power supply lines. Clamping action occurs during the transient pulse,
>>>> turning on the diode and fast triggering SCR structures when the voltage
>>>> on the input line exceeds one VBE threshold above the V+ supply (or one
>>>> VBE threshold below the V- supply). Therefore, the SP724 operation is
>>>> unaffected by poor power supply regulation or voltage fluctuations
>>>> within its operating range."
>>>>
>>>> Cheers
>>>>
>>>> Al
>>>>
>>>>
>>>> tintronic wrote:
>>>>> Al,
>>>>>> When I used to design for automotive I generally used a series
>>>>>> resistor and an SCR clamp like an SP720 (...)
>>>>> Surely you meant a TVS (Transient Voltage Supressor) instead of SCR
>>>>> (Silicon Controlled Rectifier), right?
>>>>>
>>>>> merapcb,
>>>>>>> Also, by the way, what is the best way of protecting the external
>>>>>>> RS232 lines from unwanted (accidental) voltages getting
>>>>>>> connected?
>>>>> I guess, like assumed by Al, you don't mean to protect the device against a wrong connection but against voltage spikes.
>>>>>
>>>>> I agree that series resistor and TVS bypass should be an adequate solution. I'd add ferrite beads in series too.
>>>>>
>>>>> Regards,
>>>>> Michael K.
>>>>>
>>>>> --- In m...@yahoogroups.com, OneStone wrote:
>>>>>> You're welcome, the link doesn't work for me. When I used to design for
>>>>>> automotive I generally used a series resistor and an SCR clamp like an
>>>>>> SP720 (which I think is now discontinued) or the SP724. These could
>>>>>> handle typical automotive load dumps, unlike some other possible
>>>>>> solutions which were not designed to deal with such high energy loads.
>>>>>> They are available from Littlefuse. The SP724 is a quad array.
>>>>>>
>>>>>> Al
>>>>>>
>>>>>> merapcb wrote:
>>>>>>> Folks,
>>>>>>>
>>>>>>> Thanks to all for the various ideas and insights about this issue.
>>>>>>> After deliberation it was decided to use UART0 (by re configuring from I2C when needed and then back to I2C). MUX can be done with 4052 as Al suggested. Thank you Al.
>>>>>>>
>>>>>>> I have posted the schematic of the proposed solution here:
>>>>>>> http://tinyurl.com/lmn8k5
>>>>>>>
>>>>>>> Comments are most welcome, I have not used this before so I hope I got it right.
>>>>>>>
>>>>>>> Also, by the way, what is the best way of protecting the external RS232 lines from unwanted (accidental) voltages getting connected? (automotive environment). Diodes? Series resistors?
>>>>>>>
>>>>>>> Thanks
>>>>>>>
>>>>>>> PS - Pay attention to he nifty way of being able to connect more than one device to the same port (not at the same time) and having it sensed (well, nifty I think so)
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> ------------------------------------
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>



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