As long as the PLC is RUN, it is considered to be connected. It is generally used to drive the program that runs on power-on!
There are also some instructions in Mitsubishi (especially the rules in the sequence function diagram), some things can not be placed directly with the left bus.
The m8000 is used to achieve direct intersection with the left bus, and does not delay the normal operation of the program. M8000 When your PLC RUN is running, it is turned on. It is the flag. The function of PLC operation is generally applied to the starting point of the bus.
Here, I will see the part of the sequence function diagram.
Of course, most of what you can see is the program that is used to drive the power to run, or the program that needs to run when plc is running normally. Because some errors will stop plc, although the plc has electricity, the program can not run.