Computer Interfacing
Discussions about interfacing and electronics

RS485 in multipoint communication.

Problem of RS485 in multipoint communication.


       Computer Interfacing Forum Index -> RS422 and RS485
Author Message

Feb 20, 2010 11:54 am

I have connected 5 no.s instruments on RS485 bus. I used 4 core twisted pair shielded cable for interconnection between scales and PC.
When PC is polling all machines and all machines are on, the system works OK. But when i swich off either machine on network, the communication gets halted and observed that MAX485 ic starts heating. I have used 680E resistor to pull up D+ line and Pull down D- line at each machine end. I also tried 180E termination resistance on bothe ends of network but still it not worked.

can anybody tell me where i m going wrong?? Please help.

Mar 13, 2010 8:11 pm


AS per my knowledge, only one device can drive the line at a given instant of time. When not in use, the drivers of the equipment communicating over the line must go into high impedance state.

What happens when you turn OFF your machine? Does it load the line thereby resulting into the situation you are into. I hope this helps

Apr 19, 2010 12:38 pm

I am using two rs232 to rs485 convertor and want to get them in one single rs232 channel usnig multidropping and other convertor but this causes data collision and 40 % of times data gets distorted and bad. can somebody tell me the reason. ???
New User

Joined: 31 Dec 2014
Posts: 1

Dec 31, 2014 12:59 pm

Hello all,

I'm stuck. I need to run a RS-422 signal approx. 500ft and then split it to be distributed to 4 laptop workstations.

My initial thoughts are to convert the signal to ethernet and run STP to a 5 port ethernet switch. My only concerns are that I won't be able to utilize the data at the laptops in an ethernet format.

Does anyone have any suggestions?


       Computer Interfacing Forum Index -> RS422 and RS485
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