Klockner-Moeller PS316 Program

I have been tasked with replacing a Obsolete Klockner-Moeller PS316 Modular PLC with a Mitsubishi Q series PLC and although im familiar with mitsibishi i havent had very much experiance with Klockner-Moeller. looking through the program i have noticed a lot of rungs which are similar to the following

-I/I------( )
M131 M131
-I/I------>>JCN LAB-0054
M131

I understand that the second rung is a conditional jump to label 54 within the program when M131 is false but i dont understand why they try to set the output on the previous rung.
Is this something to do with the way KM plcs Scan the program?
Any help or thoughts would be appriciated
Many thanks
Andy

Looks to me like they set up to jump to the label on every other scan. Do some of the rungs jump on set? That may help confirm that they were trying to optimize scan times. If they did you'll have to watch for routines that may depend on this "every other" execution whether they intended them to or not.

The key will be understanding the machine functions very well and programing to that and not worrying so much about the precious code.

In it's day, the 316 was pretty fast so I'm not exactly sure why they would do this. If I remember the refresh of comms may depended on the program scan time as well so that may be something to check.

Good luck!

As far as i can see there isnt any jump on set rungs but Looking into the information a little furthur it was previously converted from an PS22 to the PS316

I can feel a lot of head scratching comming on