GE 90-30 PLC User Manual

Page 76

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GFK-1084B

Chapter 3 Programming Communications Requests

Rung # 1

: Input LANIFOK (bit 16 of the LAN Interface Status bits) monitors the health

of the Ethernet Interface. If it is OK to send a COMMREQ, the HEALTHY coil is ON.
HEALTHY is used as an interlock for Rungs 3-6.

Rung # 2

: Input BEGREAD triggers READREQ, which enables execution of the MOVE

and COMMREQ functions. READREQ is a one-shot coil, activating once when BE-
GREAD transitions from OFF to ON.

Rung # 3

: The MOVEWORD function moves a zero to the CRS word referenced in the

Command Block (see rung #4). This clears the CRS word. This rung also resets the FT
output coil of the COMMREQ Function Block in rung #6.

It is vital that the CRS Status Word be cleared and the COMMREQ fault output coil be
cleared each time before initiating a COMMREQ function.

Rungs # 4-5

: The BLKMVINT functions set up the COMMREQ Command Block con-

tents. When these rungs are activated, the constant operands are moved into the
memory beginning at the address indicated in the instruction. The constant operands in
this example are defined in the Establish Read Channel Example in Section 3 of this
chapter.

Rung # 6

: The COMMREQ Function Block has 3 input parameters and one output pa-

rameter.

H The IN field points to the starting location of the Command Block parameters

(%R00301 in this example).