Mitsubishi MELSEC Q Series Programming Manual page 550

CHKST,CHK
(2) Depending on the designated contact, the CHK instruction undergoes processing identical
to that shown for the ladder below:
TO
X
Max. 150 contacts
Example X
X + 1
Y
Executes the same processing
as the ladder indicated above
(3) Numbers 1 to 150 from the vertical bus on the left side have been allocated as contact
numbers during failure detection.
(4) Reset SM80 and SD80 prior to forcing the execution of the CHK instruction.
After the execution of the CHK instruction, it cannot be performed once again until SM80
and SD80 have been reset.
(The contents of SM80 and SD80 will be preserved until reset by user.)
(5) A CHKST instruction must be placed before the CHK instruction.
An error will be returned if an instruction other than the LD, LDI, AND or ANI instruction is
used between the CHK instruction and the CHKST instruction.
(6) The CHK instruction can be written at any step of the program.
However, there is a limit in the number of uses of the CHK instruction.
• Can be used up to two places in all program files being executed.
• Can be used only one place in a single program file.
An error will be returned if the CHK instruction is used exceeding the number of uses
specified above.
7-176
X
Coil No. 1
X0
X 1
Coil No. 2
Y 0
Coil No. 3
Coil No. 4
Coil No. 5
Coil No. 6
X5 X7
Contact No. 1 2
CHKST
CHK
(Detection by both advance and retraction end sensors
during advance operation of the conveyor)
X X +1 Y
(Detection by both advance and retraction end sensors
during retract operation of the conveyor)
X +1 Y
X
(Advance operation of the conveyor at the detection
by the advance end sensor)
Y
X
(Retract operation of the conveyor at the detection
by the retraction end sensor)
Y X +1
(Advance operation of the conveyor during no detection
by the retraction end sensor)
Y X +1
(Retract operation of the conveyer at the detection
by the advance end sensor)
Y
X
X9 X1A X1C
3 149 150
SET SM80
MOV Failure No. 1 SD80
SET SM80
MOV Failure No. 2 SD80
SET SM80
MOV Failure No. 3 SD80
SET SM80
MOV Failure No. 4 SD80
SET SM80
MOV Failure No. 5 SD80
SET SM80
MOV Failure No. 6 SD80
CHK
(Error code: 4235)
(Error code: 4235)