Experimental Physics and
Industrial Control System

Bob Gunion <[email protected]> · Wed, 30 May 2012 10:55:02 -0700

I am writing a soft ioc to talk with an Allen-Bradley CompactLogix L33ER PLC.  Everything works fine except I cannot read elements of a DINT array.  I have a tag is defined in the PLC as "DINTs" with a type like DINT[4], and records like:

record(ai, "TEST_DINT0")
{
	field(SCAN, ".1 second")
	field(DTYP, "EtherIP")
	field(INP, "@plc DINTs[0]")
}
record(ai, "TEST_DINT1")
{
	field(SCAN, ".1 second")
	field(DTYP, "EtherIP")
	field(INP, "@plc DINTs[1]")
}
record(ai, "TEST_DINT2")
{
	field(SCAN, ".1 second")
	field(DTYP, "EtherIP")
	field(INP, "@plc DINTs[2]")
}
record(ai, "TEST_DINT3")
{
	field(SCAN, ".1 second")
	field(DTYP, "EtherIP")
	field(INP, "@plc DINTs[3]")
}

By cranking up the debugging output I can see the proper values being read by the scanner, but they never make it into the RVAL field of the pvs.  If I specify four separate tags (DINT0, DINT1, etc), the values do make it into the pvs.  So there's a problem with specifying the array element.

Digging through the code, I have found that the analyze_link function in devEtherIP.c detects the element index specification and, on line 899, sets pvt->special |= SPCO_INDEX_INCLUDED.  In ai_read (line 1139 of the same file), the tag value is retrieved into the pv only if pvt->special < SPCO_PLC_ERRORS; otherwise the record is marked as UDF.  This looks like a bug, unless I'm doing something wrong.

Is anyone else using this package to read arrays of DINTs (or REALs, etc)?  Am I missing something?

Thanks,
Bob Gunion

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System