I may be misunderstanding, but I don't see how my method makes that any more likely. The PB bit is only cleared if it is held for 2 seconds (or whatever time is programmed). The HMI clears the bit any time someone releases it, which would also happen if someone else was using a 2nd HMI somewhere.
Rupej your idea is clean, efficient and is easy when you have a lot of push buttons to manage. It can work well in a project, but I've come across a few that didn't.
It matters what you are doing with the input PB bit (trigger or hold an action), and where that is in your ladder code (before or after the clear, in the scan).
Scenario A:
PB #1 is pressed, then just before two seconds is up PB #2 is pressed.
PB #2 will be immediately cleared, being held high for a very short period of time.
That has a few outcomes:
1) Any ladder code for PB #2 after the PB clear will not run. Obvious yes, but when there are more than 1 PLC programmers you can't control everything.
So, I assume that this issue won't occur because it's easy to find in a code review.
2) There is no feedback to the HMI that the PB press was valid. The HMI uses the PB tag as a feedback. With a short time of PB #2 being held high there is no feedback that the PB press was valid.
3) The parallel PB input can work for push buttons that
trigger an action in the PLC. But it cannot work for push buttons that
hold an action.
Both cases are a Momentary PB in the HMI (set 1 on press, clear 0 on release).
It's the hold action of an HMI momentary PB that would cause a problem; with multiple HMIs.
PB #1 would cause the hold action of PB#2 to be very short.
Scenario #2
4) If PB #1 is pressed for 1 second, then before that is released you have PB #2 pressed for 1 second. The timer would never stop and ends up clearing all PB bits 1 second into the PB #2 press. That is an issue for push buttons with a hold action.
You could increase the timer to 5 or 10 seconds, and reduce the chance of problems. That can work for a lot of projects, as long as you are mindful of the issues.