Experimental Physics and
Industrial Control System

Mark Rivers <[email protected]> · Wed, 9 May 2012 16:28:29 +0000

Hi Pierrick,

> The download site has a link to V2.4, but what is there for downloading only goes to V2.3;
> nonetheless, there is V2.4 documentation.  Where is it?

Modbus R2-4 has not been released yet.  I just updated the following Web pages to make that more clear by changing the release date to May XXX, 2012.

http://cars9.uchicago.edu/software/epics/modbus.html

http://cars9.uchicago.edu/software/epics/modbusReleaseNotes.html

I recently added support for passing status information to callbacks in I/O Intr scanned records.  This allows input records that have SCAN=I/O Intr to have their alarm status and severity set correctly when there are communications errors to the Modbus device.  This is an important and frequently requested improvement.  However, it requires asyn R4-19, which has not been released yet either.

I plan to release asyn R4-19 and modbus R2-4 soon, but I'm hoping that a few more people can test these new features before I do.

If you'd like to help test, then you can get the latest versions of asyn and modbus via Subversion here:

https://svn.aps.anl.gov/epics/asyn/trunk/

https://subversion.xor.aps.anl.gov/synApps/modbus/trunk/

I am fairly confident these new versions are working fine, but I'd like to hear of any problems.

> I have a read command that I only want to perform once, how can I do so? It wants to 
> continue polling.

There is no way to do that.  You can make your poll interval as long as you'd like within the limits of a 32-bit signed integer in ms, which works out to about 24 days.  The overhead of doing a poll is very small, and your record will only process if the value has changed.

> I can't find any sample code for writing.  Specifically, I want to write (and read) from the
> analog output holding registers for my device (40001-4999) with function 16 (and 3 for read).
> Are there any examples from which I can glean?  I would like to see both the database entries
> as well as the drvModbusAsynConfigure commands.

There are lots of examples of writing.  Please look at the Koyo1 examples in the test IOC, modbus/iocTest/Koyo1.cmd and Koyo1.substutitions.  It shows examples of using function codes 16 and 3.  The example database file is modbusApp/Db/intarray_out.template.

Cheers,
Mark

From: [email protected] [mailto:[email protected]] On Behalf Of Pierrick Hanlet
Sent: Wednesday, May 09, 2012 10:33 AM
To: Tech Talk
Subject: modbus questions

Hi,
First, let it be known that I'm new to modbus.

My questions are as follows:
1) The download site has a link to V2.4, but what is there for downloading only goes to V2.3;
     nonetheless, there is V2.4 documentation.  Where is it?
2) I have a read command that I only want to perform once, how can I do so? It wants to 
    continue polling.
3) I can't find any sample code for writing.  Specifically, I want to write (and read) from the
    analog output holding registers for my device (40001-4999) with function 16 (and 3 for read).
    Are there any examples from which I can glean?  I would like to see both the database entries
    as well as the drvModbusAsynConfigure commands.

Thank you,
Pierrick 

"Whether you think you can or think you can't, either way, you are correct" -- Henry Ford
_______________________________________________________________
Pierrick Hanlet
IIT/Fermilab
+1-630-840-5555 (FNAL)
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System