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COMMREQ
Use the Communication Request (COMMREQ) function if the program needs to communicate with an intelligent module, such as a Genius Communications Module or a Programmable Coprocessor Module.
Note
The information presented on the following pages shows the format of the COMMREQ function. You will need additional information to program the COMMREQ for each type of device. Programming requirements for each module that uses the COMMREQ function are described in the module’s documentation.
The COMMREQ function has three input parameters and one output parameter. When the COMMREQ function receives power flow, a command block of data is sent to the intelligent module. The command block begins at the reference specified using the parameter IN. The rack and slot # of the intelligent module is specified in SYSID.
The COMMREQ may either send a message and wait for a reply, or send a message and continue without waiting for a reply. If the command block specifies that the program will not wait for a reply, the command block contents are sent to the receiving device and the program execution resumes immediately. (The timeout value is ignored.) This is referred to as NOWAIT mode.
If the command block specifies that the program will wait for a reply, the command block contents are sent to the receiving device and the CPU waits for a reply. The maximum length of time the PLC will wait for the device to respond is specified in the command block. If the device does not respond within that time, program execution resumes. This is referred to as WAIT mode.
The Function Faulted (FT) output may be set ON if:
1.The specified target address is not present (SYSID).
2.The specified task is not valid for the device (TASK).
3.The data length is 0.
4.The device’s status pointer address (part of the command block) does not exist. This may be due to an incorrect memory type selection, or an address within that memory type that is out of range.
Command Block
The command block provides information to the intelligent module on the command to be performed.
The address of the command block is specified for the IN input to the COMMREQ function. This address may be in any
Chapter 4 Series |
