User Manual Owner's manual

Publication 1785-UM024B-EN-P - January 2003
B-10 Backup States
No SFC information is included in the Force Tables
checksum. Also, note that you cannot perform forcing on
DIF or DOF files.
– Status File - This checksum is calculated for various
configured words in the Status File, and continues to be
calculated when the backup system is qualified. This allows
status to be available regarding whether the Status File
checksums differ for a qualified backup system. The different
words included in the Status File checksum for equivalence
checking are:
• Watchdog Set Point
• Fault Routine Number
• STI Set Point
• STI Routine Number
• I/O RESET Bits
• I/O INHIBIT Bits
• PII Routine Number
• PII Word Number
• PII AND Mask
• PII Polarity Mask
• PII Counter Preset
• Data Table Protection File Number
• ControlNet Backup Configuration and Status File Number
• ControlNet PLC-2 File Number
• MCP I/O Disable Word
• MCP INHIBIT Word
• MCP File Numbers
You can selectively enable equivalence checking for none,
some, or all of the 6 of the equivalence check areas, with one
exception: the Program File Structure and Program File
checksum is dependent on the Data Table Structure. Thus, if you
select the Program File Structure and Program File equivalence
check, you should also select the Data Table Structure
equivalence check.
Equivalence checking is only performed during qualification.
Once a PLC-5 system passes qualification, it does not become
disqualified even if the checksums for an area are different and
the equivalence checking for that area is enabled. For example,
if the Program File Structure and Program File equivalence
check is enabled and there is a qualified secondary, you can edit
the program files on either system without causing the
secondary system to disqualify. However, if one of the PLC-5
systems goes out of Run mode and back into Run mode and a
qualification occurs, an equivalence check failure during
qualification causes a major fault to be declared for the
qualifying system. Therefore, when performing edits on either