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I like to design a single master, several slave (up to 100) application and looking for a reliable (up to 30meter) multi drop bus. One or two lane is preferred, I will use daisy chain topology therefore USB is not suitable and also it is an overkill.

My data rate is low and intermittent, once every 3-5 sec and probably <10KB. The slaves are not synchronized.

I thought about using RS232 and implement an algo where slave transmits if there is no traffic. (Similar to Ethernet). I prefer something a bit more robust.

Also, current thinking is to wake all slaves when master transmit where all slaves receive the message, they all parse it but the one we targeted takes action. Not very efficient but it would work.

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RS422 related maybe. Certainly not RS232 –  Russell McMahon Feb 20 '12 at 2:46
    
Most of the suggestions below (so far) are based on use of RS422 differential signalling in various ways and/or protocols that build on top of it. If you want to "roll your own" you'll find RS422 an excellent place to start looking. Hardware is available and well priced and performance under various loadings and distances is well described in the literature. –  Russell McMahon Feb 20 '12 at 3:49
    
RS422 or 485 are nice but not enough for up to 100 nodes, I have to insert several bridge points to achieve high number of nodes. Could these be hacked for more nodes? –  Ktc Feb 20 '12 at 8:45

3 Answers 3

up vote 2 down vote accepted

Most of the suggestions so far are based on use of RS422 differential signalling as per my original comment, used in various ways and/or protocols that build on top of it. If you want to "roll your own" you'll find RS422 an excellent place to start looking. Hardware is available and well priced and performance under various loadings and distances is well described in the literature.

RS422 - [Pandoras box]( all link to web pages) RS422 multidrop as above

QUICK REFERENCE FOR RS485, RS422, RS232 AND RS423

Wikipedia RS422

Maxim tutorial 723Selecting and Using RS-232, RS-422, and RS-485 Serial Data Standards

TI RS422 products page - very valuable - even if you don't use their ICs ultimately Cross Reference - Application Notes - Training - Tools & Software - Block Diagrams Analog eLAB ™

They say

  • Texas Instruments is the world leader in RS-422, with a selection of transceivers for any application. TI provides industry-standard RS-422 solutions for industrial automation, motion control, e-meters, security electronics, building automation and hundreds of other applications where robust communication with high noise-immunity is needed over long cable lengths. TI offers RS-422 with multiple drivers/receivers in a single package and multiple temperature ranges.

RS485.COM - Commercial page but VERY useful

Their FAQ

RS485 links


NatSemi RS485 application notes

NatSemiRS485 overview

Other:

Basic 422 intro

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The standard serial multidrop busses are RS-422, RS-423, and RS-485. I'm not sure if these are what you want, but it is certainly a good place to start.

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One popular bus in the automobile and industrial fields is CAN Bus. It is also being used in the marine industry where it is implemented as part of NMEA 2000.

A related standard is LIN bus, which is often used with CAN and is a slower and cheaper sub-network.

There is also a super version of CAN with dual backbones for redundancy being used by BMW and others (sorry, can't remember the name of that version).

All three of these buses inter-operate and have wide support from major semiconductor manufacturers. Since this is designed for safety systems in automobiles, chips are cheap and available in extended temperature ranges. Many microcontrollers have CAN on-board.

Here is a TI whitepaper, Introduction to the Controller Area Network (CAN)

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