need help-max487 based multiple transmitter & single receiver networking

[tapasparua]

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.

 

[JimB]

Your problem is that by connecting the OE pin to +5v, the transmitter is enabled all the time.
So that when one transmitter sends data, the line is loaded by the other (non sending) transmitter and the data is corrupted.

You need to keep the OE (Output Enable) pin low, and only set it high when you want to transmit.

You will also get a problem of both outstations transmitting at the same time.
To overcome this problem, you must "listen" to the line using the receiver in the MAX487 to see that there is no signal on the line before you transmit.

JimB

 

[be80be]

JimB over look that -1 I hit the +1 great reply sorry it did the wrong thing
Dumb iPhone sorry JimB going to see if I can get a mod to fix it

 

[JimB]

Looks like a Mod fixed it.
The sins of the iPhone are forgiven.
JimB