HMI and hard-wired push buttons. Simultaneous operation.

[Zes]

Hello!

I have a control panel with two hard-wired push buttons. One button to switching on, and another one to switching off. And I have an HMI with one button to switching on/off (toggle). For some reasons I can't use two separate buttons on HMI. So I need to implement simultaneous operation with HW-buttons and HMI-button.

Here is my code for FB that alternates two outputs from one input:

All variables are boolean type.

(* Asynchronous reset. *)
IF (RST) THEN
	A := FALSE;

(* Normal operation. *)
ELSE
	A := A XOR (CLK AND NOT(M));
	Q01 := CLK AND A;
	Q02 := CLK AND NOT(A);
	M := CLK;	
END_IF;

And here is my diagram for simultaneous control:

The problem is if coil was turned on with HW-button, it takes two pushes to turn it off with HMI-button. Maybe I need to add small changes to handle this issue:

(* Asynchronous reset. *)
IF (RST) OR (SET) THEN
	A := NOT RST;

(* Normal operation. *)
ELSE
	A := A XOR (CLK AND NOT(M));
	Q01 := CLK AND A;
	Q02 := CLK AND NOT(A);
	M := CLK;	
END_IF;

But maybe I missing something, this approach is wrong and there is more suitable and simple solution. Any advice, recommendations or thoughts will be greatly appreciated.
All buttons are momentary. 'SwitchedOn' is sealed internally in 'FB_L'.

 

[amberman]

Does your HMI button start/stop have to be toggle or can it be momentary? If the latter you can use a one shot from it in series with the "switched on" bit so it can mimic a start or stop button depending on whether the machine has started or not.

 

[JesperMP]

Why separate hardwired on/off buttons, and for the HMI a toggle button ?
Just keep the user interface consistent.
Choose separate buttons or toggle buttons for both.

I do not like the toggle button, but if you do go that way, I would add de-bounce timers.

 

[Zes]

Unfortunately I can't. In this particular project I must strictly follow to all requirements. One of them is two separate HW-buttons and one on a HMI.

 

[amberman]

Unfortunately I can't. In this particular project I must strictly follow to all requirements. One of them is two separate HW-buttons and one on a HMI.

But does it have to be a toggle switch on the HMI? If not then use a momentary and you should be able to do it no problem.

 

[rdrast]

Use your single button on the HMI to implement a toggle on a state bit in the PLC.
Use the physical buttons to unconditionally latch or unlatch the state bit.
Use the state bit as an indicator for the HMI.