Omron G9SP Series Manual page 19

- 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) Once 300 ms has elapsed, the RS-232C reception end bit (X0A) 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.
(4) To store the reception response in D100, the INPUT instruction is executed.
(5) G9SP communications reception data is set to the send command from X 100 and echo
back bit.
(6) The send command is transferred to the RS-232C send port, which enables sending to
the G9SP-series Controller.
(7) The checksum and the end code 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.
(8) The timer is restarted and the next receive processing is performed after 300 ms.
(9) The checksum calculation subroutine given above is called, and the checksum of the
reception response is calculated.
(10) The checksum of the reception response and the end code are checked, and the G9SP
Communications Transmission Data is copied to Y 200 and G9SP Safety Input Terminal
Data is copied to Y 220.
2 - 2 RS-232C Serial Communications
Description
2
2-9