In comp.arch.embedded,
rickman <gnuarm@gmail.com> wrote:
>> second-source OR roll my own.
>
> I don't think you will find that I2C is intended for hot-swap.  I am
> not saying it can't be done, I am saying that it has no built-in
> support.  The one-wire interface uses a CRC to verify communications
> and in general is intended for noisy or intermittent communications
> and supports hot-swap.

We did a schematic once with external I2C through an LTC4303 buffer
which is designed for hot-swap I2C applications. The external I2C
was dropped befor the actual board was made, so no real experience
with this buffer. If we go for I2C, I suspect I will have another
look at it.

> The one-wire spec is a bit tricky to read for timing, but the info is
> all there.  The only real issue in rolling your own is the timing.  An
> MCU will likely be run on an internal RC oscillator and will need to
> have some margin of stability and accuracy.  The timing margins are
> pretty wide to handle this, so the RC oscillators on many MCUs will be
> good enough, but you need to pay attention to this detail.  Otherwise
> the protocol is not difficult at all.
>
> I bet you can even beat the Dallas price on many one-wire devices and
> end up with a smaller footprint as well (other than the cap and the
> diode).

If we go with the 1-wire, I think well go with the standard parts at
first, but having the option of emulating a part is nice. That leaves
our option to bigger memories open and solves the single source issue.

-- 
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

On Jul 21, 4:35 am, Stef <stef...@yahooI-N-V-A-L-I-D.com.invalid>
wrote:
> In comp.arch.embedded,
>
>
>
> Anton Erasmus <nob...@spam.prevent.net> wrote:
> > On Fri, 18 Jul 2008 17:20:42 +0200, Stef
> ><stef...@yahooI-N-V-A-L-I-D.com.invalid> wrote:
>
> >>For production of measurement probes, we need to store calibration data
> >>on them. Because of the limited number of connections, the 1-wire
> >>memories look like good candidates. For now we need at least 16kbit of
> >>storage which should be eprom or eeprom. The only suitable device from
> >>maxim therefore seems to be the DS2505 with 16kbit eprom. (the larger
> >>ones are serialized 'uniqueware' devices). In the I-button range are 2
> >>candidates, a 64kbit eprom and a 32kbyte eeprom, but these are rather
> >>expensive (but the sealed housing is nice though).
>
> >>Because of the limited selection and whish for second source, I'm
> >>looking for another manufacturer that makes 1-wire memories, but have
> >>not found one yet.
>
> >>Are there any other manufacturers of these devices? Maybe they use
> >>different names for the bus as is the case with I2C vs. "Two Wire
> >>Interface".
>
> > Microchip has started a range with what they call a UNI/O bus.
>
> Interesting, but unfortunately completely incompatible with the dallas
> bus. Also not bus-powered so needs 3 wires instead of 2. But that may
> be cured as others have written in other replies.
>
> Biggest chip is 16kbit, enough but no future expansion. Other nice
> feature of the dallas chips is de unique ID, not required, but nice to
> have.
>
> There also seems to be no second source for UNI/O memories, or does
> someone know of any?
>
> It looks like the only second-source option would be using I2C, but
> that requires 4 pins on the connector, or maybe 3 if it can be made
> bus-powered. Any experiences with I2C and hot swap?
>
> So it looks like I will have: 2-pin connector OR 3-pin connector OR
> second-source OR roll my own.

I don't think you will find that I2C is intended for hot-swap.  I am
not saying it can't be done, I am saying that it has no built-in
support.  The one-wire interface uses a CRC to verify communications
and in general is intended for noisy or intermittent communications
and supports hot-swap.

The one-wire spec is a bit tricky to read for timing, but the info is
all there.  The only real issue in rolling your own is the timing.  An
MCU will likely be run on an internal RC oscillator and will need to
have some margin of stability and accuracy.  The timing margins are
pretty wide to handle this, so the RC oscillators on many MCUs will be
good enough, but you need to pay attention to this detail.  Otherwise
the protocol is not difficult at all.

I bet you can even beat the Dallas price on many one-wire devices and
end up with a smaller footprint as well (other than the cap and the
diode).

Rick

In comp.arch.embedded,
rickman <gnuarm@gmail.com> wrote:
> On Jul 18, 11:20 am, Stef <stef...@yahooI-N-V-A-L-I-D.com.invalid>
> wrote:
>>
>> Are there any other manufacturers of these devices? Maybe they use
>> different names for the bus as is the case with I2C vs. "Two Wire
>> Interface".
>
> I've never seen any other sources, but the protocol is simple enough
> that you can make your own devices using a very tiny MCU.  It probably
> won't be able to be line powered, but it could be lower cost.  Some of
> the Dallas 1-wire parts are not very cheap.  But a diode (or an LDO)
> and capacitor might work to make a low end MCU line powered.

If I can get it line-powered, this would be an interesting option. And
with rolling your own, you're not limited to a particular protocol as
well. ;-)

-- 
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

In comp.arch.embedded,
Anton Erasmus <nobody@spam.prevent.net> wrote:
> On Fri, 18 Jul 2008 17:20:42 +0200, Stef
><stef33d@yahooI-N-V-A-L-I-D.com.invalid> wrote:
>
>>For production of measurement probes, we need to store calibration data
>>on them. Because of the limited number of connections, the 1-wire
>>memories look like good candidates. For now we need at least 16kbit of
>>storage which should be eprom or eeprom. The only suitable device from
>>maxim therefore seems to be the DS2505 with 16kbit eprom. (the larger
>>ones are serialized 'uniqueware' devices). In the I-button range are 2
>>candidates, a 64kbit eprom and a 32kbyte eeprom, but these are rather
>>expensive (but the sealed housing is nice though).
>>
>>Because of the limited selection and whish for second source, I'm
>>looking for another manufacturer that makes 1-wire memories, but have
>>not found one yet.
>>
>>Are there any other manufacturers of these devices? Maybe they use
>>different names for the bus as is the case with I2C vs. "Two Wire
>>Interface".
>
> Microchip has started a range with what they call a UNI/O bus.  

Interesting, but unfortunately completely incompatible with the dallas
bus. Also not bus-powered so needs 3 wires instead of 2. But that may
be cured as others have written in other replies.

Biggest chip is 16kbit, enough but no future expansion. Other nice
feature of the dallas chips is de unique ID, not required, but nice to
have.

There also seems to be no second source for UNI/O memories, or does
someone know of any?

It looks like the only second-source option would be using I2C, but
that requires 4 pins on the connector, or maybe 3 if it can be made
bus-powered. Any experiences with I2C and hot swap?

So it looks like I will have: 2-pin connector OR 3-pin connector OR
second-source OR roll my own.

-- 
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

On Jul 20, 3:25=A0pm, rickman <gnu...@gmail.com> wrote:
> On Jul 20, 7:32 am, Rocky <RobertG...@gmail.com> wrote:
>
>
>
>
>
> > On Jul 18, 11:47 pm, rickman <gnu...@gmail.com> wrote:
>
> > > On Jul 18, 11:20 am, Stef <stef...@yahooI-N-V-A-L-I-D.com.invalid>
> > > wrote:
>
> > > >> > Are there any other manufacturers of these devices? Maybe they u=
se
>
> > <SNIP>
>
> > > > different names for the bus as is the case with I2C vs. "Two Wire
> > > > Interface".
>
> > > I've never seen any other sources, but the protocol is simple enough
> > > that you can make your own devices using a very tiny MCU. =A0It proba=
bly
> > > won't be able to be line powered, but it could be lower cost. =A0Some=
 of
> > > the Dallas 1-wire parts are not very cheap. =A0But a diode (or an LDO=
)
> > > and capacitor might work to make a low end MCU line powered.
>
> > > Rick
>
> > One can even skip the diode - use the internal diode on the pin. Maybe
> > parallel a few pins on a 6 pin PIC could be used to increase the
> > typical 10mA rating for the internal diodes. Just add the cap across
> > the supply.
> > Rocky
>
> Doesn't that create a possibility of latch-up? =A0Then the MCU would be
> inactive until the cap drained. =A0I've never actually tried doing this,
> have you?
>
> Rick

I have tried it inadvertenly. The circuit worked OK, but obviously if
is preferable to have all the VDD pins wired !

IIRC the latchup current is in the order of hundreds of mA. The rated
current into a pin is 20mA on the 16F88x range. (Checked the data
sheet.) One could put a 220 ohm resistor in series which would keep
the current limited, but I imaging it would be more to limit the drive
current from the main microcontroller than to protect the '1 wire'
unit.

Also, by the time the voltage got to a level to support latchup the
current would have dropped significantly.

Rocky

On Jul 20, 7:32 am, Rocky <RobertG...@gmail.com> wrote:
> On Jul 18, 11:47 pm, rickman <gnu...@gmail.com> wrote:
>
> > On Jul 18, 11:20 am, Stef <stef...@yahooI-N-V-A-L-I-D.com.invalid>
> > wrote:
>
> > >> > Are there any other manufacturers of these devices? Maybe they use
>
> <SNIP>
>
> > > different names for the bus as is the case with I2C vs. "Two Wire
> > > Interface".
>
> > I've never seen any other sources, but the protocol is simple enough
> > that you can make your own devices using a very tiny MCU.  It probably
> > won't be able to be line powered, but it could be lower cost.  Some of
> > the Dallas 1-wire parts are not very cheap.  But a diode (or an LDO)
> > and capacitor might work to make a low end MCU line powered.
>
> > Rick
>
> One can even skip the diode - use the internal diode on the pin. Maybe
> parallel a few pins on a 6 pin PIC could be used to increase the
> typical 10mA rating for the internal diodes. Just add the cap across
> the supply.
> Rocky

Doesn't that create a possibility of latch-up?  Then the MCU would be
inactive until the cap drained.  I've never actually tried doing this,
have you?

Rick

On Jul 18, 11:47=A0pm, rickman <gnu...@gmail.com> wrote:
> On Jul 18, 11:20 am, Stef <stef...@yahooI-N-V-A-L-I-D.com.invalid>
> wrote:
>
> >> > Are there any other manufacturers of these devices? Maybe they use

<SNIP>

> > different names for the bus as is the case with I2C vs. "Two Wire
> > Interface".
>
> I've never seen any other sources, but the protocol is simple enough
> that you can make your own devices using a very tiny MCU. =A0It probably
> won't be able to be line powered, but it could be lower cost. =A0Some of
> the Dallas 1-wire parts are not very cheap. =A0But a diode (or an LDO)
> and capacitor might work to make a low end MCU line powered.
>
> Rick
>
One can even skip the diode - use the internal diode on the pin. Maybe
parallel a few pins on a 6 pin PIC could be used to increase the
typical 10mA rating for the internal diodes. Just add the cap across
the supply.
Rocky

Stef wrote:
> For production of measurement probes, we need to store calibration data
> on them. Because of the limited number of connections, the 1-wire
> memories look like good candidates. For now we need at least 16kbit of
> storage which should be eprom or eeprom. The only suitable device from
> maxim therefore seems to be the DS2505 with 16kbit eprom. (the larger
> ones are serialized 'uniqueware' devices). In the I-button range are 2
> candidates, a 64kbit eprom and a 32kbyte eeprom, but these are rather
> expensive (but the sealed housing is nice though).
> 
> Because of the limited selection and whish for second source, I'm
> looking for another manufacturer that makes 1-wire memories, but have
> not found one yet.
> 
> Are there any other manufacturers of these devices? Maybe they use
> different names for the bus as is the case with I2C vs. "Two Wire
> Interface".
> 
> 
You are not likely to.  It is owned by Maxium.  I do not know if they 
have second sources.

On Jul 18, 11:20 am, Stef <stef...@yahooI-N-V-A-L-I-D.com.invalid>
wrote:
> For production of measurement probes, we need to store calibration data
> on them. Because of the limited number of connections, the 1-wire
> memories look like good candidates. For now we need at least 16kbit of
> storage which should be eprom or eeprom. The only suitable device from
> maxim therefore seems to be the DS2505 with 16kbit eprom. (the larger
> ones are serialized 'uniqueware' devices). In the I-button range are 2
> candidates, a 64kbit eprom and a 32kbyte eeprom, but these are rather
> expensive (but the sealed housing is nice though).
>
> Because of the limited selection and whish for second source, I'm
> looking for another manufacturer that makes 1-wire memories, but have
> not found one yet.
>
> Are there any other manufacturers of these devices? Maybe they use
> different names for the bus as is the case with I2C vs. "Two Wire
> Interface".

I've never seen any other sources, but the protocol is simple enough
that you can make your own devices using a very tiny MCU.  It probably
won't be able to be line powered, but it could be lower cost.  Some of
the Dallas 1-wire parts are not very cheap.  But a diode (or an LDO)
and capacitor might work to make a low end MCU line powered.

Rick

On Fri, 18 Jul 2008 17:20:42 +0200, Stef
<stef33d@yahooI-N-V-A-L-I-D.com.invalid> wrote:

>For production of measurement probes, we need to store calibration data
>on them. Because of the limited number of connections, the 1-wire
>memories look like good candidates. For now we need at least 16kbit of
>storage which should be eprom or eeprom. The only suitable device from
>maxim therefore seems to be the DS2505 with 16kbit eprom. (the larger
>ones are serialized 'uniqueware' devices). In the I-button range are 2
>candidates, a 64kbit eprom and a 32kbyte eeprom, but these are rather
>expensive (but the sealed housing is nice though).
>
>Because of the limited selection and whish for second source, I'm
>looking for another manufacturer that makes 1-wire memories, but have
>not found one yet.
>
>Are there any other manufacturers of these devices? Maybe they use
>different names for the bus as is the case with I2C vs. "Two Wire
>Interface".

Microchip has started a range with what they call a UNI/O bus.  

Regards
  Anton Erasmus