Procedure for Programming

Procedure for Programming

(Original Document)

Procedure to Follow

The array below shows the procedure for programming the application.

Step	Action	Details
1	Preparing the communication port.	Change the Slave Modbus mode to Character mode by sending a WRITE_CMD to the serial port. For a modem transmission , send the HAYES command by using the PRINT_CHAR block to configure the modem. For a modem transmission , send the HAYES command by using the PRINT_CHAR block. The dial message is used to send a telephone number to the modem.
2	Master Modbus mode	Switch to Modbus Master mode using the WRITE_CMD command. Send data to write on the Slave PLC.
3	Reseting the communication port.	Switch to Character mode using the WRITE_CMD command. For a modem transmission, send the escape character, then send the disconnect command to send a disconnection message to the modem by using the PRINT_CHAR block. Return to the starting mode of the serial port (Slave Modbus) using the WRITE_CMD command.

Writing the Command Words

The following steps should be executed to send a WRITE_CMD to a communication port:

Step	Action	Detail
1	Test to determine whether any command is pending.	Before executing a WRITE_CMD, test whether an exchange is currently in progress using the EXCH_STS language object (%MWr.m.c.0). To refresh this word, use the READ_STS block.
2	Assign the command word.	You must next modify the value of the command language object in order to perform the required command. For a Modbus link, the object language is the internal word CONTROL (%MWr.m.c.24). For example, to switch from Modbus mode to character mode, the bit 14 of the word %MWr.m.c.24 is set to 1. Note: A single command bit must then be switched from 0 to 1 before transmitting the WRITE_CMD.
3	Send the command	Finally, a WRITE_CMD must be executed to acknowledge the command.

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