Release R2-0 of the EPICS "modbus" module is now available. This
release removes the limitation of only being able to communicate with a
single Modbus slave address from an asyn serial port or TCP port. The
new release can communicate with any number of slaves from a single asyn
port, which allows, for example, multiple Modbus devices on a
daisy-chained RS-485 bus.
Thanks very much to Yves Lussignol at CEA in France who made these code
NOTE: This release requires all Modbus startup command scripts to be
changed, because the syntax of the modbusInterposeConfig and
drvModbusAsynConfigure commands has changed. The slave address
parameter has been removed from modbusInterposeConfig and added to
drvModbusAsynConfigure. For this reason it has been given a new major
release number (R1-3 to R2-0).
The release notes are here:
The documentation is here:
The tar file is here:
Please let me know of any problems or questions.
From: firstname.lastname@example.org [mailto:email@example.com]
Sent: Friday, November 27, 2009 7:36 AM
To: Mark Rivers; firstname.lastname@example.org
Subject: !RE: Modbus help
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,
> -----Original Message-----
> From: Mark Rivers [mailto:email@example.com]
> Sent: 25 November 2009 18:35
> To: Shepherd, Emma (DLSLtd,RAL,DIA); firstname.lastname@example.org
> Subject: RE: Modbus help
> 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.
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