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Chapter 6
Troubleshooting
Errors Indicated by Diagnostic
Bits
Summary
6 2
The block lengths of read- and write-block-transfer instructions should
be equal (PLC-2 family processors); or if they are different lengths, do
not enable the read and write instruction in the same scan.
Your conditioning instructions in block-transfer rungs allow the rungs
to turn off and on.
If you're using a PLC-2/30 processor, set the scanner for block-transfer
operation.
If you're using a PLC-3 processor, create block-transfer data files.
Examine the diagnostic bits by displaying the read block of the
block-transfer-read instruction. Refer to the programming manual of your
processor for the procedure.
The lower byte of the first read-data word contains the diagnostic bits.
If this bit is set:
07
The module is not receiving +5V from the input power supply;
check the supply and the connections between the supply and
the module.
06
The module has not received any block transfer write data;
check your block transfer instructions.
04
The module has examined all 16 presets (it has received write
data) and has found a preset that is not in BCD; check bits 03
through 00 for the error code to determine which word contains
the incorrect preset. See Appendix D for the error codes.
If you have followed the wiring and installation guidelines in chapter 3
and the block-transfer guidelines in chapter 4, you have minimized the
need to troubleshoot your encoder module. If you need to troubleshoot,
however, the information in this chapter can help you diagnose and
correct problems.
Then:
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