Self-Diagnostics Function - Mitsubishi Q2ACPU User Manual

9. MAINTENANCE FUNCTION
9.3

Self-diagnostics Function

The self-diagnosis function is a function whereby the QnACPU diagnoses its own errors.
(1)
(2)
(3)
(4)
The self-diagnosis function serves to prevent malfunctions of the PLC, and to
facilitate preventive maintenance. Self-diagnositics processing is executed if an error
occurs at QnACPU power ON or while the PLC is in the RUN status, and it involves
the display of the error detected by the self-diagnostics function, stopping of PLC
operation, etc.
The QnACPU stores the error code corresponding to the error that has occurred in
special register SD0, turns the ERROR LED on, and displays an error message on
the LED indicator.
If several errors occur, the error code of the latest error is stored in SD0.
Even if the PLC power is turned OFF, the latest 16 errors are recorded with the
battery backup. (Refer to Section 9.4.)
The PLC diagnostics mode of the GPP function can check error histories.
When an error is detected by self-diagnosis, CPU module operation complies with
one of the following two modes:
• Mode in which PLC operation is stopped
When an error is detected, operation is stopped immediately and all outputs (Y) are
turned OFF.
• Mode in which PLC operation is continued
When an error is detected, only the program part affected by the error is not
executed; the rest of the program is executed.
In addition, settings can be made in PC RAS setting in the parameter mode to
continue operation or stop operation when the following errors occur:
1) Calculation (including SFC programs)
2) Extended Ins
3) Fuse Blown
4) I/O Unit Compare
5) Sp Unit Access
6 IC Card Access
7) IC Card Operate
(The default for all of these in the parameters is "Pause".)
Example: If "Resume" is set for I/O module verify error, operation is continued using
I/O address before error occurrence.
When an error is detected, a record of the error occurrence is stored in the special
relays (SM0, SM1) and the error contents are stored in a special register (SD0). Use
these special relays and this special register in the sequence program to establish
PLC or mechanical system interlocks.
9 - 4