Initial Startup Detection

Does anyone have an idea of how to run a set of functions once as soon as the PLC comes up after a power on - a start up function??

The PLC in question is a Mitsubishi Alfa AL2-24MR-D

Thanks,
Gerry....

Not that familiar with the alpha 2 series, but Bit M08 pulses when transiting from STOP to RUN. I would try using this bit as most PLC's begin power-up in the STOP mode before going into a RUN condition.

A simple way that works on any PLC... but uses up one input:

Wire 24 vdc to an input (or what ever your input uses ie: sinking, sourcing, etc.)

When the program runs through the first scan, it will see the input is on. You use this and a one-shot to set a bit.

Since there is a one shot, it will only be true for the first scan of the ladder.

Although most PLCs have some sort of status bit to indicate the "First Pass".

The 'set of functions' questions begs to either a timer, or the start of some sort of sequencer.
What I do in Allen Bradley is have the very first run of the main program be XIC S:1/15 JSR FirstScan, -or- XIC S:FS JSR FirstScan.
The SECOND rung is a TON with no conditions...say 30 seconds.

The first run in FirstScan is a timer RESET command. In other words, the timer RESETS on first scan, and then times all the time, in the main.

My most common use is to reset the DeviceNet scanner after a few seconds, and then, make the scanner RUN after its reset (a few seconds longer).

Yes, if your PLC does not have a FIRST SCAN bit, you have to resort to some hardware trick.