Re: [foxboro] Modbus Communications

I may be mis reading your problem but you can have lots of transactions
So 42001 can be RW with the others write only
Note transaction rates are read rates all writes happen straight away
Some devices wont alow span read over non used registers creating the
need for even more transactions or write single commands.

One thing to comment on here is the 224 gives a lot more control over
comms than a FDSI FBM so its more likely to go on a 224
Shaun

-----Original Message-----
From: foxboro-bounce@xxxxxxxxxxxxx [mailto:foxboro-bounce@xxxxxxxxxxxxx]
On Behalf Of Scott Matus
Sent: Tuesday, 30 September 2008 10:24
To: foxboro@xxxxxxxxxxxxx
Subject: [foxboro] Modbus Communications

When using a IOUT block can you disable/ignore the readback from the
external device?

We are trying to communicate via ModBus to a Atlas Copco Compressor
using an FBM224. The compressor came with its own controller called a
Elektronicon, but it is proprietary so a device called a Combox-S sets
between the I/A system and the compressor. Everything works well with
the exception of registers 42001,42002 and 42004, which use a function
code 06. Problem is that no matter which one of these registers send a
request(in which the compressor does respond to correctly), only 42001
gets a readback, and it is the value that was sent by the other
register. Atlas Copco is telling us that these registers in the Combox-S
use a shared register and the Foxboro System needs to ignore the
readback. If this is true is this normal?  There are other registers
41062,41062,41064,41065 that also use the function code 06 that work as
what I call normal, only the register that sends the request gets the
readback. When setting up the transaction table there is a selection for
WRITE ONLY a
 nd one for READ/WRITE.  When selecting WRITE ONLY it does not establish
communications with the Combox-S.



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