Hi,
I Have the same requirement of demultiplexing one serial port into
multiple, and one of the serial port should be selected depending on the
input select signals. I used 74HC4051 8 channel multiplexer or
demultiplexer. It can be applied to both analog and digital multiplexing
and demultiplexing. 
I used the GPIO pins for the select signals (s0,s1,s2) and the enable
pin.
and i have given the TX pin of my device to Z input. 

But, unfortunately the data is coming on all the output pins of 74hc4051
IC.
Is there any other way of demultiplexing the TX and multiplexing the RX
pin.

Any suggestions would be appreciated.

Thanks,
somu. 

In article <KpCdnZWfD_Z_GBDbRVnyiQA@pipex.net>, 
steve@NOSPAMTAfivetrees.com says...
> TT_Man wrote:
> > "Marra" <cresswellavenue@talktalk.net> wrote in message
> > news:1183506500.717357.187590@o61g2000hsh.googlegroups.com...
> >> On 3 Jul, 10:16, ElderUberGeek <aribl...@gmail.com> wrote:
> >>> Hi. I have only one available UART on a micro but need to connect
> >>> two serial devices (chips on the same board). Is there some type of
> >>> chip that can be used that will accept two serial inputs and then I
> >>> can use a GPIO pin to switch between the sources? The two serial
> >>> sources need not be used together (meaning when one is being used,
> >>> the other is not required).
> >>>
> >>> Thanks
> >>
> >> If both dont communicate at same time a simple and gate would do the
> >> trick.
> >>
> > Simpler than that.... a few diodes as he doesn't have concurrent I/O
> > conflicts....Rxd on Micro may need a pullup...
> >
> > Tx1 -I<I------I------ RXd on Micro
> >                    I
> > Tx2 -I<I------I
> >
> > Tx on Micro---I-------Rxd1
> >                        I------Rxd2
> 
> If you're dealing with a breadboard, maybe. For a product, in SMT, not 
> so sure. One logic device may be cheaper to put down (and allow a more 
> reliable design) than a handful of diodes.
> 
> To the OP: if your protocol is master/slave, and you can guarantee no Rx 
> unless your Tx demands a response, then just mux both at the UART I/O. 
> If you have multiple possible concurrent Rx sources, you're out of luck. 
> UART the fastest and bit-bang the slowest.
> 
>
That's a good point.  When I muxed  my serial port,  one device was
a satellite transceiver that had it's own buffer, and was primarily 
a send-only device.  The other device was a GPS, which I could set
up once at the beginning  and read at any time.  I only needed the
GPS data about once each 5 minutes,  as oceanographic buoys aren't
supposed to move too far in that time frame.  They were much better
candidates for multiplexing than the control console port, which could
receive user input at any time.

Mark Borgerson

TT_Man wrote:
> "Marra" <cresswellavenue@talktalk.net> wrote in message
> news:1183506500.717357.187590@o61g2000hsh.googlegroups.com...
>> On 3 Jul, 10:16, ElderUberGeek <aribl...@gmail.com> wrote:
>>> Hi. I have only one available UART on a micro but need to connect
>>> two serial devices (chips on the same board). Is there some type of
>>> chip that can be used that will accept two serial inputs and then I
>>> can use a GPIO pin to switch between the sources? The two serial
>>> sources need not be used together (meaning when one is being used,
>>> the other is not required).
>>>
>>> Thanks
>>
>> If both dont communicate at same time a simple and gate would do the
>> trick.
>>
> Simpler than that.... a few diodes as he doesn't have concurrent I/O
> conflicts....Rxd on Micro may need a pullup...
>
> Tx1 -I<I------I------ RXd on Micro
>                    I
> Tx2 -I<I------I
>
> Tx on Micro---I-------Rxd1
>                        I------Rxd2

If you're dealing with a breadboard, maybe. For a product, in SMT, not 
so sure. One logic device may be cheaper to put down (and allow a more 
reliable design) than a handful of diodes.

To the OP: if your protocol is master/slave, and you can guarantee no Rx 
unless your Tx demands a response, then just mux both at the UART I/O. 
If you have multiple possible concurrent Rx sources, you're out of luck. 
UART the fastest and bit-bang the slowest.

Steve
http://www.fivetrees.com 

"Marra" <cresswellavenue@talktalk.net> wrote in message 
news:1183506500.717357.187590@o61g2000hsh.googlegroups.com...
> On 3 Jul, 10:16, ElderUberGeek <aribl...@gmail.com> wrote:
>> Hi. I have only one available UART on a micro but need to connect two
>> serial devices (chips on the same board). Is there some type of chip
>> that can be used that will accept two serial inputs and then I can use
>> a GPIO pin to switch between the sources? The two serial sources need
>> not be used together (meaning when one is being used, the other is not
>> required).
>>
>> Thanks
>
> If both dont communicate at same time a simple and gate would do the
> trick.
>
Simpler than that.... a few diodes as he doesn't have concurrent I/O 
conflicts....Rxd on Micro may need a pullup...

Tx1 -I<I------I------ RXd on Micro
                    I
Tx2 -I<I------I

Tx on Micro---I-------Rxd1
                        I------Rxd2 

On 3 Jul, 10:16, ElderUberGeek <aribl...@gmail.com> wrote:
> Hi. I have only one available UART on a micro but need to connect two
> serial devices (chips on the same board). Is there some type of chip
> that can be used that will accept two serial inputs and then I can use
> a GPIO pin to switch between the sources? The two serial sources need
> not be used together (meaning when one is being used, the other is not
> required).
>
> Thanks

If both dont communicate at same time a simple and gate would do the
trick.

ElderUberGeek wrote:
> Hi. I have only one available UART on a micro but need to connect two
> serial devices (chips on the same board). Is there some type of chip
> that can be used that will accept two serial inputs and then I can use
> a GPIO pin to switch between the sources? The two serial sources need
> not be used together (meaning when one is being used, the other is not
> required).

As has already been said, "You haven't provided enough information."

If the two chips need to communicate to each other, and one needs to 
communicate with the outside world but the other does not, then look at 
an SPI between the chips. Is likely your MCUs already have SPI modules, 
if not its terribly easy to make in software. Especially easy when you 
are writing both ends.

If both MCUs need to communicate to the outside world, consider daisy 
chaining. Connect one to the RxD coming in, its TxD to the other MCU's 
RxD, and the 2nd MCU's TxD to the outgoing TxD. The first MCU keeps 
everything it recognizes and passes the rest and new data it has created 
to the second. The second MCU keeps everything it recognizes and passes 
the rest to the outside connector while possibly adding some new data.

Daisy chaining requires no additional hardware, only a bit of software.

In article <1183454182.314158.61410@g37g2000prf.googlegroups.com>, 
aribloch@gmail.com says...
> 
> Hi. I have only one available UART on a micro but need to connect two
> serial devices (chips on the same board). Is there some type of chip
> that can be used that will accept two serial inputs and then I can use
> a GPIO pin to switch between the sources? The two serial sources need
> not be used together (meaning when one is being used, the other is not
> required).
> 
> Thanks

In a similar situation,  I used at TI  TS3L110DR    IC LAN switch.

It's basically a quad 1 of 2 multiplexer with the added advantage
that the ports are bidirectional.   

Mark Borgerson

"ElderUberGeek" <aribloch@gmail.com> wrote in message
news:1183454182.314158.61410@g37g2000prf.googlegroups.com...
>
> Hi. I have only one available UART on a micro but need to connect two
> serial devices (chips on the same board). Is there some type of chip
> that can be used that will accept two serial inputs and then I can use
> a GPIO pin to switch between the sources? The two serial sources need
> not be used together (meaning when one is being used, the other is not
> required).
>
> Thanks
>

I used a 74126, but it was not so intuitive as both TX and RX must
stay high while idle. When you switch one of the sources off you have
to make sure it doesn't pull the line down. (we're talking about 0/5V)
A relay works either.

If you have 2 spare GPIO you can implement it in software.

In comp.arch.embedded,
ElderUberGeek <aribloch@gmail.com> wrote:
>
> Hi. I have only one available UART on a micro but need to connect two
> serial devices (chips on the same board). Is there some type of chip
> that can be used that will accept two serial inputs and then I can use
> a GPIO pin to switch between the sources? The two serial sources need
> not be used together (meaning when one is being used, the other is not
> required).

If you can leave both connected to Tx, you can switch Rx with a single
7400. If your Rx's remain quiet when not in use and they are open drain,
you can just connect them together. Both assuming you are dealing with
logic levels.


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