Omron G9SP Series Manual page 25

- Checksum Calculation Subroutine
Step
(1) The fixed portion of the send command is set. This processing is performed once at startup.
(2) A communications refresh timer of 300 ms is started. This performs the first sending after
300 ms.
(3) To execute the sending and receiving of the RS232C port, the RS instruction is executed.
(4) Once 300 ms has elapsed, to execute the transmission processing, the pulse is set to M0.
(5) Once 300 ms has elapsed, the RS-232C reception end bit (M8123) is checked, and receive
processing is performed if data has been received. A send command from the Standard
PLC is initially required, and so reception processing is performed after completing the first
send.
(6) The checksum calculation subroutine given above is called, and the checksum of the
reception response is calculated.
(7) The checksum of the reception response and the end code are checked, and the G9SP
Communications Transmission Data is copied to Y200 and G9SP Safety Input Terminal
Data is copied to Y220.
(８) G9SP communications reception data is set to the send command from X 100.
(９) The checksum calculation subroutine given above is called, and the checksum of the
transmission command is calculated.
(10) The checksum are set to the transmission command.The send command is transferred to
the RS-232C send port, which enables sending to the G9SP-series Controller.
(11) The timer is restarted and the next receive processing is performed after 300 ms.
2 - 2 RS-232C Serial Communications
Description
2
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