ABB unlatch coil with its own bit

I have a program that goes like this
contact latches a coil and unlatches itself
b1
--l l----------(l)c1
(u)b1

then C1 does this
C1 C1
----l l-----(u)

it unlatches itself?
can someone explain this to me?

Is there any logic between those rungs? If not then seems pointless to me.

If there is logic in between, it could be related to a HMI pushbutton or something similar.

With a HMI's momentary pushbutton, it's not like a physical PB which holds an input high as long as you hold the button on. When you press the button, the HMI sends a message to the PLC, saying "set bit x to 1". Then, when you release the button, the HMI sends another message to the PLC, saying "set bit x to 0". If that second message gets dropped, your button is now stuck on. For this reason, any time I use a button on a HMI, I have the PLC immediately turn the button back off, and set a different bit for one scan - and that's the bit I use throughout my code for "button pressed".

This could be something similar: when B1 is activated, turn it straight back off and turn on bit C1. After the rest of the logic does whatever it needs to do, with the knowledge that B1 was activated, C1 gets turned off as well.

Of course, if there's nothing in between those two rungs, then as robert said - seems pretty pointless.

thanks a lot guys, I figured out it should be related to wanting the input only momentarily available independent of the time the user pushes the button (there was logic in between the two lines) . I was troubleshooting a system that is programmed in India, and they make quite bit of mistakes, so many that sometimes I have to doubt If something is programmed on purpose or by mistake.

it could be grafcet or line scan programming.

james