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ADM2485 parameters for RS485

Question asked by pshah on Apr 22, 2015
Latest reply on Apr 23, 2015 by Dirk

Hi There,

We are using ADM2485 for use of RS485 Transceiver for MODBUS communication. I have questions on this chip about following parameters.

 

What is the maximum length it supports in RS485 network (Daisy chain)? What gauge? Must be shielded?

What should be baud rate in general for this chip? Is it possible to give table for baud rate vs distance?

What is proper Termination resistor values for Daisy Chain network?

What are the other factors or parameters need to be considered?

 

Here is what we are using: -

Baud Rate = 9600kbps

Cable Gauge = 24 (CAT-5)

Termination resistor = 150ohm

Cable type = Twisted Pair for A and B lines and one for Ground.

 

I would like to tell you that, when I hook-up three of our instruments, it works fine but when I go beyond three device in Daisy Chain Net-work, it stops communication. Any idea what could be the reason?

 

I was looking other manufacturer's ICs (similar to ADM485) and they have provided most of the information that I am asking this post. Where can I find this for ADM2485?

 

Any help or input will be greatly appreciated.

 

Thank you in advance,

 

pj

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