User`s manual

A-2 Series 90™-30 CPU with Embedded PROFIBUS Interface – November 2004 GFK-2334A
A
COMMREQ Ladder Instruction
A Communications Request is initiated when a COMMREQ ladder instruction is activated
during the PLC scan. At this time, a command from the PLC via the Communications
Request is sent to the PROFIBUS device.
At the conclusion of every request, the CPU reports the status of the request to the Status
Word, which is a location in PLC memory that is designated by the Status Word Pointer in
the Command Block.
The COMMREQ ladder instruction has four inputs and one output:
Enable Input: Must be Logic 1 to enable the COMMREQ Instruction. It is recommended that
the enabling logic be a contact from a transition (“one-shot”) coil.
IN: The memory location of the first word of the Command Block. It can be any valid
address in word-type memory (%R, %AI, or %AQ). For example, %R00100 at IN would
indicate that the starting address of the Command Block is %R00100.
SYSID: A hexadecimal value that gives the rack and slot location of the target device. The
high byte (first two digits of the hex number) contains the rack number, and the low byte
contains the slot number. The SYSID for the CPU366/CPU367 is 01h:
SYSID
Rack Slot Hex Word Value
0 1 0001h
TASK: Must be 21 (15h) for embedded PROFIBUS
FT Output: The function’s FT (fault) output can provide an output to optional logic that can
verify successful completion of the Communications Request. The FT output can have
these states:
FT Output Truth Table
Enable Input Status Does an Error Exist? FT output
Active No Low
Active Yes High
Not active No execution Low
 The FT output is set High if:
 The specified target address is not present (for example, specifying Rack 1
when the system only uses Rack 0).
 The specified task number is not valid for the device.
 Data length is set to 0.
 The FT output can either be connected to another device, such as a set coil, or can be
left open.