Mitsubishi MELSEC Q Series Programming Manual page 551

(7) 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.
(8) The failure detection method differs according to whether SM710 is ON or OFF.
(a) 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.
(b) 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.
(9) 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.
(10) 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
(1) In any of the following cases, an operation error occurs, the error flag (SM0) turns ON, and
an error code is stored into SD0.
• There is a parallel ladder.
• There is an NOP instruction.
• There are more than 150 contact instructions.
• A CHK instruction is not executed following 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 at three places or more in all of programs being executed.
• The CHK instruction is used at two places or more in a single program.
X5 X7 X9
1 2 3
Contact No.
Does not execute check
XA X1A X1C
CHK
4
Contact numbers are allocated
CHKST,CHK
1
2
3
4
6
6
7
8
(Error code: 4235)
(Error code: 4235)
(Error code: 4235)
(Error code: 4235)
(Error code: 4235)
(Error code: 4235)
(Error code: 4235)
(Error code: 4235)
(Error code: 4235)
7-177