Author Topic: RS-232 Bus chip?  (Read 2170 times)

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Offline AsellithTopic starter

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RS-232 Bus chip?
« on: January 04, 2008, 04:26:17 PM »
I need to use one RS-232 line to control multiple peices of equipment for a project. Do they make a 3 state bus chip for RS-232 type signals? I've been having trouble finding one. For future projects it would make connecting many sensors to one controllers easier. However for this project I specifically need to control where each transmit and receive goes. Some cases I will need to send commands to one unit that will then respond but I need that responce to go to a third peice of equipment. It's kinda crazy and might now work :) If not I have a work around just not sure if I have enough memory to do it.

Johnny B
Jonathan Bowen
CorSec Engineering

Offline dunk

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Re: RS-232 Bus chip?
« Reply #1 on: January 04, 2008, 05:10:06 PM »
so i have no personal experience with RS422 but i believe it may be what you are looking for.
the search term you are looking for in searches is "multi drop".

alternatively you could prevent devices from transmitting by enabling hardware flow control and holding their CTS? line high.
this would not stop all devices on a segment from receiving what was transmitted though.
it would also be very messy. there has to be a nicer solution.

is one of your serial devices a PC? another option would be put more than one serial port in the PC and do it in software.
transmit an address before the serial data and have the PC send it out the other serial port if it's destined for the other device.

if the device at the remote end of the modem is also a PC you could configure one of the serial port based Point to Point Protocols (PPP) and do it all in software. i think SLIP does this although it's ages since i had to set up anything so antiquated.

that's all the ideas i can think of.
good luck with it.


Offline GUmeR

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Re: RS-232 Bus chip?
« Reply #2 on: January 05, 2008, 05:39:22 AM »
Read on Modbus protocol.

Offline JonHylands

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Re: RS-232 Bus chip?
« Reply #3 on: January 06, 2008, 07:32:56 AM »
The Bioloid robot uses a scheme that would probably work for what you're asking. It uses TTL level RS-232, but on a single wire, and is a multi-drop bus.

Each device has an ID, and parses every packet that comes through (and the responses), and discards any that aren't meant for it.

- Jon


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