first pass scan bit

well i fell stupid what would the first pass scan bit be in rs logix 5000?

jim cav

S:fs

One thing to keep in mind about S:FS is that each program has its own bit which is set for the first scan the first time that program executes after the pre-scan. Each program's S:FS bit is independent of any other program.

Lets say that you have several periodic tasks plus the continuous task, and the longest periodic task has a periodic rate of 5 seconds. Under each of the task are several programs. When the PLC goes to run the other programs could have executed thousands of times before the program in the 5 second periodic task gets to execute. However, after five seconds when that program finally gets to execute, any XIC in the program that is addressed to S:FS will evaluate true because it is the first scan of that program.

If you have an event task or a program that is inhibited and later enabled though a GSV then it could be hours or days (or even months) after the processor goes to run before that program first runs. When it first runs its S:FS bit will be set.

99% of the time it won't matter, but be aware that it could matter.

Knees hurt

how do i enter this

jimcav said:

how do i enter this

Click to expand...

Just use an xic...

XIC S:FS