GE GFK-1004B user manual Commreq FunctionBlock, Commreq Command Block, Channel Commands

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COMMREQ FunctionBlock

The COMMREQ Function Block is the ladder instruction that triggers the execution of the Channel Command. In the COMMREQ Function Block, you specify the rack and slot location of the Ethernet Interface and a pointer to a location in memory that con- tains the Command Block. There is also a fault output on the COMMREQ Function Block that indicates certain programming errors. See Section 2 for details.

COMMREQ Command Block

The COMMREQ Command Block is a structure that contains information about the

Channel Command to be executed. The Command Block consists of two parts:

Common Area - includes a pointer to the COMMREQ Status word (CRS word)

Data Block Area - describes the Channel Command to be executed.

When the COMMREQ function is initiated, the Command Block is transferred to the

Ethernet Interface for action.

See Section 2 for a description of the common area of the Command Block and Section 3 for details on the Data Block area and Channel Commands.

Channel Commands

The Channel Commands are a set of client PLC commands used to communicate with a server PLC.

Advantages of Channel Commands

The advantage of Channel Commands is their ability to establish a channel to execute multiple periodic reads or writes with a single initiation of a COMMREQ function. A Channel Command can also be used to execute a single read or write.

Up to 16 channels (numbered 1-16) can be established by a client PLC. The channel number is specified in the Command Block for the Channel Command. The channel can be monitored using the Channel Status bits and the Detailed Channel Status words.

See Section 3 for more information.

GFK-1004B Chapter 4 Programming Communications Requests 4-3