XXMIT Programming Rules

Programming Rules Description

It may take several PLC cycles to send a Modbus request or character string. The Start, Active, Done and Error bits operate in the following way:

The start signal is written by the application. Active, Done and Error signals are read by the application.

NOTE: If the Start signal is maintained to 1 after the completion, the XXMIT block restarts. This generates multiple transmission of the same Modbus or ASCII message to the receiving device.

CAUTION

MULTIPLE TRANSMISSION

Make sure that the XXMIT block is not restarted after completion.

Failure to follow these instructions can result in injury or equipment damage.

Resetting the Start bit as soon as the Done bit is seen at 1 prevents the XXMIT block to restart after completion.

Several XXMITs can not be activate at the same time. If more than one XXMIT is activated, the first scanned block will operate and prevent operation of all other XXMITs until it has completed. The next block in the scan that is called will generate an immediate fault code 150.

The XXMIT function block can only be used in MAST task. There is an immediate fault code (127) if it is started in the FAST / AUX or EVENT tasks (there is no control performed by Control Expert at build time).

NOTE: The XXMIT input parameter must be initialized before setting the START input. They must not be changed during the function block activity. If the START bit is reset to 0 before completion, the function block is stopped (active bit to 0). To have a complete block execution, the value of 1 must be applied on the START bit until the operation has finished or until an error has occured.