User`s manual

GFK-2334A Appendix A COMMREQ Operation A-3
A
COMMREQ Programming Requirements and Recommendations
 COMMREQ instructions should be enabled by a contact from a transition coil.
 If using more than one COMMREQ in a ladder program, verify that a previous
COMMREQ executed successfully before executing another one. This can be done
by checking the Status Word and the FT (Fault) output.
 The FT output is held False if the Enable Input is not active. This means that if the
COMMREQ is enabled by a transitional (one-shot) contact and a fault occurs, the FT
output is High for only one PLC scan. To capture the fact that a fault occurred, you
can program the fault output as a Set coil, which would not be automatically reset at
the end of a scan. Additional logic would then be needed to reset the fault output coil
after the fault is acknowledged and before the next execution of the COMMREQ.
 Programming a device, such as a Set Coil, on the FT output of the COMMREQ is
optional; this output may be left open if desired.
 It is necessary to initialize the data in the Command Block before executing the
COMMREQ instruction. Since the normal PLC sweep order is from top to bottom,
initializing the Command Block in an earlier rung (or rungs) than the rung that contains
the COMMREQ will satisfy this requirement.
 If you use MOVE instructions to load values into Command Block registers, use a
Word-type MOVE to load a hexadecimal number, and an Integer-type MOVE to load a
decimal number.