GE GFK-0787B user manual Programming for Startup

7

Programming for Startup

The PLC Subsystem chapter of this book describes the sequence of actions that occur when the PLCs in a GMR system are started up.

HThe GMR software in the PLCs only allows one PLC to come online at a time. First, a PLC determines its ID by reading the serial bus addresses of the GMR Bus Controllers (PLC A = 31, PLC B = 30, PLC C = 29). It then sets the corresponding PLC Identification status bit (see page 7-11): %M12225 for PLC A or %M12226 for PLC B, or %M12227 for PLC C.

HWhile a PLC is initializing, the GMR software sets the Inhibit status flag (%M12231). This Inhibit flag should be used to prevent the application program from executing until initialization is complete. Example ladder logic that provides this functionality is shown on page 7-18. In addition, the PLC's outputs are disabled. If outputs do not disablesuccessfully, the GMR software halts the PLC.

HIf the initializing PLC is PLC C, the GMR software automatically commands any discrete Genius blocks configured for Hot Standby operation to accept outputs from the PLC at serial bus address 29. If this function fails to complete successfully, the GMR software sets the System status flag (%M12234) to 1.

HDuring initialization, a PLC also communicates with the GMR I/O blocks and with Bus Controllers in other PLCs. If any of these communications fails, status bit %M12234, which indicates System Failure at Powerup, is turned on. The application program can use this bit as a permissive for continuing and annunciation.

HAs each PLC starts up, it checks to see whether another PLC is already online and sending outputs.

h if not, the PLC sets the ªCold Startº flag (%M12237). The application program can use this flag to initialize the application program data.

h If one other PLC is already online, the initializing PLC reads that PLC's initialization data (%M and %R). It then sets its own %M and %R initialization data areas to match. This is shown by the following simplified example:

A counter in PLC A starts

1 2 3 4 5 6 7 8 9 10 11

PLC A starts up

Time

The counter in PLC B starts

6 7 8 9 10 11

PLC B starts up and initializes its counter with PLC A

GFK-0787B Chapter 7 Programming Information 7-15