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'[PICLIST] [EE] A five-to-one RS 232 - cruncher - a'
2001\04\11@161912 by MEDICINTEKNIK KB

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Hello,

A question: 5 different devices use RS 232 as a communication protocol to/from a controller (or PC). I need to combine those lines to ONE RS 232 line.
One way to do it is to use 3 PIC's with dual ports (or 6 single port PIC's) or makbe "bit-bang" data, make up a que, and let one port become the "compressed" data stream further down the line.

however...

Ï have tried to find a commerciallay available box that is doing this magic tric - and almost suceeded. I don't have time to design the thing, and wonder if anyone out there know where I can buy one :=)

NOTE: It must be a separate box. A multiple RS 232 comm card to a PC doesn't count.

Any hint appreciated. Thank you.


Sven in Sweden

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2001\04\11@170909 by Rex's mail

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Have a look at the black box catalogue - if I underrstand your requirement
they have a 8 port RS232 expander


{Original Message removed}

2001\04\11@193902 by Bill Westfield

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   A question: 5 different devices use RS 232 as a communication protocol
   to/from a controller (or PC). I need to combine those lines to ONE RS
   232 line.

   tried to find a commerciallay available box that is doing this magic
   trick - and almost suceeded. I don't have time to design the thing, and
   wonder if anyone out there know where I can buy one :=)

What you want is called a "multiplexor."  Usually for async traffic you
want a "statistical multiplexor", which allocated trunk bandwidth to the
ports generating data at the tim, rather than a TDM box that gives every
port a slot whether it has data or not.  Lots of vendors.  (http://www.statmux.com
was one that popped up quickly.)  Not particularly cheap. "5" is likely to
be an inconvenient number...

A special case of statmuxes is a "terminal server" running a networking
protocol over a wan link of some kind.  The cheapest implementation is
likely to be a couple of obsolete PCs with multiport async cards (6 ports
worth) and linux running SLIP or PPP on one of the ports, and
telnet/telnetd things on the other ports.  Or perhaps some
couple-generations-old commercial equipment - I saw someone selling
cisco-500 terminal servers for $250 each.  One of those has 16 ports and
should do a servicable job...

BillW

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2001\04\12@055241 by Peter L. Peres

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You can do it if you have hardware handshake on all cables. Have a PIC
monitor RTS on each wire and give CTS to one box at a time, also control a
four way switch. The PIC need not 'see' the data but it needs to account
for any latency in the RTS/CTS handshake in the controllers (i.e. how many
characters go out after CTS is turned off). The TxD line from the PC can
be wired directly to all the boxes, through a buffer,  or through a switch
also. For full handshake you also need to switch DTR/DSR. It all depends
on what you are doing and how fast the data is. In any case I'd switch all
the controllers to the highest data rate to buy time for switching gaps
(at least one character).

Peter

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2001\04\12@092144 by Lawrence Lile

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Often this is accomplished with RS485 multidrop networks.  These are usually
in some kind of master-slave protocol, with the master polling the slaves
for a response.  The slaves don't have access to the RS-485 bus unless sent
an addressed message by the master.

There are RS485-RS232 converters out there.

I use a couple of temperature control systems that work this way.  I think
I2C also can work this way, although I don't understand it as well.

If you are designing both ends of the system this might suit your needs.  If
your peripheral devices are already set in stone as RS-232, then it won't
help you much.

Lawrence Lile

P.S.  RS-232 is a protocol originally named after Radio Shack: the guy who
invented the protocol went down to Radio Shack and bought $2.32 worth of
parts and voila'! he had an RS-232 converter!    ;-)


{Original Message removed}

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