Experimental Physics and
Industrial Control System

"Bob Dalesio" <[email protected]> · Wed, 25 Aug 2004 06:59:22 -0600

Hi JOhn,

The reason it is going back to 1 - is that the driver
reads the output and reflects that value in the database.
This is done as there may be a different master for the
outputs - like a Allen-BRadley PanelMate.

For outputs, it is a good idea to have the IOC write to a
boolean that is a request to drive an output. Make the
output momentary by setting the HIGH field. Have it write
to a soft variable in the PLC. Then the PLC can compute
any interlock logic necessary to determine if it is safe
to write the output.

Kay will have to say more about why the output may not be
changing.

Bob
On Tue, 24 Aug 2004 20:54:21 -0500
 "Hammonds, John P." <[email protected]> wrote:

We are starting to examine the use of ControlLogix PLCs
at IPNS and I am

looking at Kay's driver for Ethernet/IP. We now have our
first test

setup going and we are looking at some of the subtleties
with how to

access various types of tags. I am very novice with any
PLC so please

forgive my awkward use of terminology. 

It appears that the only tags that are accessible to the
EPICS driver

are ones provided at the controller level ( in RSLogix
5000 App). Is

this correct?

We have been able to access inputs (ai & bi) OK but have
been having

some trouble with binary outs. So far we have avoided
arrays

altogether. We have a binary out module ( relay out I
believe ). We

can control an output of this directly using the base tag

Local:2:O.Data[3] with a binary output record. However,
when we create

another tag which aliases Local:2:O.Data[3] and point the
record at

this, we can turn the output on but cannot turn it off.
I have an EPICS

screen that allows me to change the value and monitor the
RVAL field.

Here I see the new value (0) temporarily reflected in the
RVAL &VAL

fields but then it goes back to 1. No change is seen in
RSLogix 5000.

We can reset the Value with RSLogix 5000 and repeat the
process. The

same effect is seen for any "soft" tag. BTW the soft
records that I

have are type BOOL.

Any ideas?

John Hammonds 
Data Acquisition Systems Manager
Intense Pulsed Neutron Source
[email protected]
(630)252-5317

Bob Dalesio
[email protected]
410 557 0297 Maryland
505 699 1632 Cell Phone

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System