UART handshaking + control over 2 wire link

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Hi, i am looking at running serial comms over a bidirectional fibre
link. What i would like is to run full handshaking and control lines
over this link. Are there any chips which will do this for me?

If not, i am considering using a microcontroller to sample all the line
states, then send the bit states over the link to be reconstructed the
other end.

Any ideas or suggestions much appreciated.

Cheers,

Chris


Re: UART handshaking + control over 2 wire link
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Can you use software flow control like Xon/Xoff?

You might look up how PPP sends TCP/IP over modems to get some idea's.

You might also consider having a packet transfer system where each
packet must be acknowledged before the next packet is sent.

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Re: UART handshaking + control over 2 wire link

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I think you misunderstood. He doesn't want to do serial flow
control.

He wants to multiplex multiple signals over a single "wire". In
this case the wire is optical, but that's mostly irrelevent.

I do know of people who do this.  They run 16 high-speed serial
ports over a single wire. The modem control/status/handshake
lines are multiplexed at a much lower rate than the data lines
(KHz for the handshake lines vs. MHz for the data lines).  The
people I know that do this designed a full-custom ASIC to do
it, but I think you could probably do the same thing in an
FPGA.

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Re: UART handshaking + control over 2 wire link
Thanks for the replies. I will be controling a modem on the other end
of the fibre. I need all the serial lines so that the software sees
what it expects to see and can control the modem with DTR etc lines as
needed. Whilst i could use XON/XOFF i do also need the other lines...
hoping there was a off the shelf chip i could by to do this for me!

Cheers,

Chris


Re: UART handshaking + control over 2 wire link

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as

I guess you need chips not modules such as

http://www.robustdc.com/index.shtml?model=rdc232fo#rdc232fo


Re: UART handshaking + control over 2 wire link
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A cheap 8:1 multiplex/demultiplex that I built 30 years ago did the
transmission over several miles of twisted pair, carrying a current
loop.  The multiplexor was a UART, set to transmit with 2 stop
bits, and receive with 1. (This allowed for rate mismatches at the
ends).  Each input went to one input bit of 8, and was received on
the corresponding 1 of 8 at the other end.  What it really needed
for long term reliability was 8 stop bits on send, which
unfortunately needed added hardware.  Today I would suggest
building it all out of a single bit-banging PIC, and to turn the
bit rates up by about a factor of 4 or more.

The result was used to move 8 110 to 300 baud lines over a 9600
baud link.  Note that things are transparent, so you can use a
multiplexed line as a transparent handshaking signal if you wish.
Effectively you have:

                  +-------+               +------+
   8 lines --->---|  MX   |               | deMX |-->-- 8 lines
                  |       |-<- 2 lines ->-|      |
   8 lines ---<---| deMX  |               |  MX  |--<-- 8 lines
                  +-------+               +------+

where the '2 lines' can be one bidirectional link.

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Re: UART handshaking + control over 2 wire link
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I guess I did misunderstand.  He did add that he's controlling a modem
on the other end so that's clear now even to me.

I just didn't want him doing all the extra work if he really didn't need to.

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Another similar way to do it might be to have your two PICs (or other
micro) sending the data between themselves 4 bits at a time and using
the other bits for control signals.  That might work for him and only
run at two times the bit rate.

It seems like some micros can do a 9 bit transfer.  Would that be a way
to pass an occasional control byte now and then?

If bit 9 is 0, then its data.  Otherwise it's a flow control byte thats
only sent when the hardware lines have changed state.

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Re: UART handshaking + control over 2 wire link

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This may be a little over the top for your particular app, but there is an
internet protocol
defined in http://rfc.net/rfc2217.html to address this kind of thing.

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