need help-max487 based multiple transmitter & single receiver networking

Discussion in 'Embedded Systems and Microcontrollers' started by tapasparua, Jun 23, 2013.

  1. tapasparua

    Thread Starter New Member

    Sep 23, 2009
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    i am trying to design a microcontroller based fault detection system where a single receiver will receive any data from multiple transmitters. it is assumed that at a time only one transmitter will send the data. all microcontrollers belong to 8051 family, and have a 11.059MHz crystal. the baud rate is 9600bps. i have used max487 for the networking. now when a single transmitter is attached to the network, the receiver works. but when i add another transmitter (tot 2 transmitters & 1 receiver in the network), the receiver does not respond. i checked with logic probe that no data is reaching at rx pin of receiver. the number of transmitter will be upto 127. please suggest.
     
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  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    With the MAX487 DE pin pulled high ALL transmitters are on at once, so they are fighting each other to drive the network. As stated in the Wikipedia Article "RS-485 drivers need to be put in transmit mode explicitly by asserting a signal to the driver. This allows RS-485 to implement linear topologies using only two wires. The equipment located along a set of RS-485 wires are interchangeably called nodes, stations and devices."

    So you need a little hardware change so each slave controls DE, then a software change where the master unit requests each slave in turn to report status.
     
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