PLC to modbus Communication (RS485)

L

Thread Starter

Lewis

I am trying to find a modbus ASCII protocol so i can write the PLC code, with the specific request for coils and register, and a break down of responses so i can pick out the data i need.

Does anyone have an idea of where i could get the protocol from, or have a protocol document?

Thanks
 
T

Tommy Bryans

Hi Lewis,

www.modbus.org have all the info. I have in front of me 'Modbus over Serial Line Specification and Implementation Guide' dated Dec 20 2006 which was downloaded from the site. It contains all you need including algorithms/look-up tables for generating LRC/CRC.

Regards,
TommyB
 
K
Hi, I assume that you are writing the software in a PLC, only ask as most PLC's have modbus functions. There is a lot of stuff written about modbus serial and ethernet, if you want I can email you a manual.

Kevin
 
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