View Full Version : What is nop

July 24th, 2009, 02:41 PM
I want to know what nop 0 means th epart of the program that is using this is :

AN "M-CS/F25"
JC M002
L 0
T MW 34
T MW 36
M002: NOP 0

probably M002 is NOP 0 But what exactly this means?

July 24th, 2009, 02:45 PM
No operation

L D[AR2,P#0.0]
July 24th, 2009, 03:29 PM
A label and nop instruction are used by the editor when creating conditional logic within a rung that requires a jump to the end of the network. Nop's are also used when creating STL programs that involve jumps, the NOP is a convenient method for creating a destination for a jump instruction without creating the code required at the destination point (so you can save a partially coded block for example)

Note that if you click on an instruction and press F1, you will get the Simatic help on the instruction.

July 28th, 2009, 12:09 AM
S5 world history:
It's form the time when the EPROM was program memory.
NOP0 lives 16 bit to false state and later you can write new command over it and write it to EPROM without erasing whole EPROM.
NOP1 writes all 16 bits to true state for same reason, as like deleting some command(s).

July 28th, 2009, 11:23 AM
In S5 the nop also was used in stl so that things could also be displayed in ladder, for example
A I 0.0
LKT 10.0
A T 0
= F 0.0
The nop replaced the other parameters in the timer function.
also some people filled large areas of blocks with nop's when doing fixed jumps so that if a few extra lines of code were required they did not have to change the fixed jump address.