Experimental Physics and
Industrial Control System

<[email protected]> · Fri, 27 Nov 2009 13:36:19 -0000

Hi all,

Just a quick thanks to everyone for their helpful suggestions.  In the
end I dismantled the rack and connected the IOC directly to the RS485
terminals on one of the devices and the modbus comms worked perfectly.
It looks like an issue with the daisy chain wiring.

Keep me updated with the V2-0 status Mark - if I can get this wiring
fixed I'll be your first customer!

All the best,
Emma

> -----Original Message-----
> From: Mark Rivers [mailto:[email protected]] 
> Sent: 25 November 2009 18:35
> To: Shepherd, Emma (DLSLtd,RAL,DIA); [email protected]
> Subject: RE: Modbus help
> 
> 
> Emma,
> 
> Once you get the communication with a single device working, 
> you are going to run into problems trying to communicate with 
> multiple RS-485 devices through a single serial port.  The 
> reason is that I am using the asynInterposeInterface layer to 
> add the RTU header with the slave address.  But asyn only 
> allows a single interposeInterface for each asyn port, which 
> restricts one to a single slave address.
> 
> Yves Lussignol from CEA has fixed this problem, by moving the 
> slave address management to layer 2 (asyn port driver) from 
> layer 3 (interpose interface).  He sent me a modified version 
> of the driver with this fix back in March 2009, but I have 
> been remiss in not testing it and releasing a new version of 
> the driver.  It does change the syntax of the 
> drvModbusAsynConfigure command, so it will be a major 
> release, i.e. 2-0.
> 
> I will try to get a new release out in the next couple of weeks.
> 
> Mark
> 
> 

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System