Basic SFC Functions
4-14. 【NOP】,【END】
Mnemonic Function Format and Devices: None
NOP No operation
(No
Operation)
or null step
Devices: None
END Force t
(END)
he
current
program scan
to end
Devices: None
Description
z When clear the whole program, all the instructions become NOP. If add
NOP instructions between the common instructions, they have no effect
and PLC will keep on working. If add NOP instructions in the program,
n modify or add programs, the step vary will be decreased. But
with NOP instructions, then the
PLC repeatedly carry on input disposal, program
executing and output disposal. If write END
instruction at the end of the program, then the
instructions behind END instruction won’t be
executed. If there’s no END instruction in the
When debug, insert END in each program
segment to check out each program’s action.
Then, after confirm the correction of preceding
block’s action, delete END instruction.
Besides, the first execution of RUN begins with
END instruction.
then whe
the program should have rest quantity.
z If replace the program’s instructions
When executing END instruction, refresh monitor timer. (Check if scan cycle is a long timer. )
program, the PLC executes the end step and then
repeat executing the program from step 0.
OUT→NOP
AND→NOP ANI→NOP
Contacts short circuit
OR→NOP
ORI→NOP
Open circuit
62
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