Honeywell IPC 620-0080 is the Processor Module for the 620-25 or 620-35 processor systems. Parts may be ordered as individual components or as a processor system package.

The 620-0080 processor provides computing power to the PLC, and computes memory checksum and other diagnostic functions to verify system integrity.

The checksum calculation and comparison check occurs in the processors with Firmware Revision 50 (V.R. 2.2) as follows:

1. The processor calculates the initial checksum of the user program during the retentive scan.
2. The processor calculates a second checksum of user program while program is running by reading six memory words per scan. If any on-line changes occur, flag bits are set to cause the processor to start over by recalculating the initial checksum.
3. If the two checksum calculations match the process starts over since no error has been detected.
4. If the two checksum calculations do not match, the processor sets the error flag and is forced to the PROGRAM mode. The Loader/Terminal will display a PC Diagnostics Fail message. The recovery procedure for a checksum error is to reload program memory. The 623-51 will display "program checksum error" when the processor is placed in PRGM mode.

For a complete list of IPC 620 parts visit IPC 602 PLC