Function block for the MODBUS networking Fieldbus driver:

• The Runtime Service maintains a queue of MODBUS transactions.
• This function block delivers information about received requests from the list.
• The function block refers to one MODBUS slave configuration.

Inputs

Outputs

Remarks

The last 4 received requests are remembered in a queue inside the MODBUS stack. This functionality works for read or write of bits or registers.

A request is identified by function code, MODBUS address and number of items.

At most 4 requests received are stored in between 2 PLC scans. If more, then oldest ones are lost.

ST Language

MBSReq is a declared instance of MBSLAVELASTREQ block.

MBSReq (TRUE, ‘MyConfig’);

diFunc := MBSReq.function;

diModbusAddr:= MBSReq.addr;

diNbModbusItem:= MBSReq.nb;

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