Thanks to everyone for all your quick replies.

"10 ways to bulletproof 485 "
http://www.national.com/apnotes/A...rface.html
Erik

i got it, thank you, just have to read it now. I also searched these forums and have found similar threads, but I have yet to find a schematic or sample code.
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3. Forgive me, this may sound like a stupid question, but would the software routines for rs485 use the same uart routines in the 89C51, and just add a rs485 transceiver? I can't find any info on this on the internet.
The very same with one exception: you need to control the direction pins.
Erik

it would really help if I could see some source code and a schematic. I am capable of sending rs232 data between 2 micros and I have the working source for that.

I downloaded the data sheet for Maxim's max485.
I am **assuming** ( i could be WAY OFF) that the TX and RX on the 89C51 would connect to the max485 as follows:

DI driver input connect to TX on 89C51 ?
RO receiver output connect to RX on 89C51 ?
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How far apart are these 5 micros
On the same PCB?
Within the same box?
Within the same rack?

millimetres? inches? feet? yards? miles...?

50-75 feet apart. They are going to be used for security monitoring, lights, cameras, other devices within my property. This is just a home project that I want to build myself.

I would like to see a schematic if anyone knows where I can view one online. That would certainly simplify things a great deal.
Thanks
Charles