Mitsubishi Electric MELSEC-Q/L Programming Manual page 525

• Place LD and AND instructions prior to the CHK instruction to establish a check condition. Check conditions cannot be set
using other contact instructions. If a check condition has been set with LDI or ANI, the processing for the check condition
they specify will not be conducted. However, contact numbers during failure detection can also be allocated to the LDI and
ANI instructions.
X5 X7 X9 XA
1 2 3
Contact No.
• The failure detection method differs according to whether SM710 is ON or OFF.
• If SM710 is OFF, checks will be conducted of coil numbers 1 to 6 for each contact successively. When the CHK instruction is executed, checks will be in order
from coil No. 1 of contact No. 1, through coil No. 6, then move on to contact No. 2 and check the coils in order from No. 1. The CHK instruction will be
completed when coil No. 6 from contact No. n has been checked.
• If SM710 is ON, checks will be conducted of contact numbers 1 through n, in coil number order. When the CHK instruction is executed, checks will begin with
the ladder for coil No. 1, in order from contact No. 1 until contact No. n, then move on to the coil No. 2 ladder and begin from contact No. 1. The CHK
instruction will be completed when a check has been made through contact No. n of coil No. 6.
• If more than one failure is detected, the number of the first failure detected will be stored. Failure numbers detected after
this will be ignored.
• The CHK instruction cannot be used by a low speed execution type program. If a low speed execution type program has
been set in a program file containing the CHK instruction, an operation error will be returned, and the CPU module
operation will be suspended.
Operation error
• In any of the following cases, an operation error occurs, the error flag (SM0) turns ON, and an error code is stored into SD0.
Error Error details
code
4235 There is a parallel ladder.
There is an NOP instruction.
There are more than 150 contact instructions.
A CHK instruction is not executed after the CHKST instruction.
The CHK instruction is executed when no CHKST instruction has been
executed.
The CHKST and CHK instruction are used in a low speed execution type
program.
There is an instruction other than the LD, LDI, AND or ANI instruction
between the CHK instruction and the CHKST instruction.
The CHK instruction is used on three or more points in all of the program
files being executed.
The CHK instruction is used on two more points in a single program file.
Does not execute check
X1A X1C
CHK
4
Contact numbers are allocated
Q00J/ QnH QnPH QnPRH
Q00/
Q01
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7 APPLICATION INSTRUCTIONS
7.10 Debugging and Failure Diagnosis Instructions
7
QnU LCPU
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523