Configuring Screen Maker Buttons from a Digital Input

At the digital-input terminal, voltage and input current must remain inside the module rating; excess electrical load is a hardware problem, while the button-selection symptom is a timing and state-ownership problem. Map both touch commands and changes of system on auto to the same paired assignments: select Button-1 by setting A and resetting B, and select Button-2 by setting B and resetting A. Bind each button’s displayed selection to those signals rather than to an independent touch-only state. Choose explicitly whether the maintained DI has continuous priority or acts only when it changes state.

Input State and Symptom Limits

The number that matters is the count of active selections. With two mutually exclusive choices, the valid steady-state count is exactly one: either A is true and B is false, or B is true and A is false. A count of zero produces no selection; a count of two produces conflicting selections.

Separate the electrical input from the interpreted state. The field signal first passes through the DI sensing circuit, where applied voltage drives current and creates thermal load. The controller or HMI then reads a logical value through an input image, tag, or communication update. This is heat at the hardware boundary and logic after the input image.

If the physical input indicator changes but system on auto does not, inspect input mapping and communications. If the tag changes and A/B do not, inspect the control logic. If the signals change correctly but the screen does not, inspect button feedback bindings and display refresh.

Competing Writers and Scan Timing

A touch button and a DI-driven routine are two writers targeting the same state. The final value depends on execution order whenever they issue different commands during the same scan or communication interval. A maintained DI routine that writes every scan will overwrite a manual touch command almost immediately, even though the button works correctly when tested without DI control.

HMI refresh, controller scan, communications polling, and input filtering occur on separate schedules. A brief intermediate state can therefore appear if one signal is updated before the other. Treat selection as one transaction: every command writes both signals as a pair. Setting only the requested signal and relying on another routine to clear the opposite signal creates windows in which both can be true.

The visual button state is another possible writer if the object maintains an internal latch. Use the object as a command source and display the confirmed value of A or B. This makes the screen show the controlled state instead of remembering only the last touch.

Control-Strategy Selection

Use level control when the DI must always dictate the selection. While system on auto is true, continuously command A true and B false; while it is false, command the opposite pair. Manual operation may still generate commands, but those commands cannot persist against the maintained DI state.

IF system on auto = TRUE:
    SET A
    RESET B
ELSE:
    RESET A
    SET B

Use transition control when the DI must behave like an operator action. A false-to-true transition performs the Button-1 action once, and a true-to-false transition performs the Button-2 action once. A later manual selection then remains active until the DI changes again. This interpretation best preserves meaningful manual control while still reproducing both button actions from the input.

On false-to-true transition of system on auto:
    SET A
    RESET B

On true-to-false transition of system on auto:
    RESET A
    SET B

If operations require a manual override, define its priority as a separate operating rule rather than allowing execution order to decide. The screen should indicate which source currently owns the selection so that an operator can distinguish a rejected command from a failed button.

Shared-Action Configuration Procedure

1. Confirm the DI status changes reliably at the input module. Compare the measured field voltage with the module’s documented thresholds and ratings if the indication chatters or never changes.
2. Confirm system on auto follows the physical DI at the location where the selection logic executes. Check tag mapping and the communication path if the two states differ.
3. Create one logical action for selecting Button-1: set A and reset B. Configure the manual Button-1 touch and the DI true event or level to invoke that same action.
4. Create the complementary action for selecting Button-2: set B and reset A. Configure the manual Button-2 touch and the DI false event or level to invoke it.
5. Bind the selected appearance of Button-1 to A and the selected appearance of Button-2 to B. Remove any independent display latch that can disagree with these signals.
6. Select level control or transition control and document the priority. Place the paired assignments in one execution location so another routine cannot reverse only half of the transaction.
7. Initialize the pair to one valid state at startup. If the runtime starts while the DI is already true, transition-only logic also needs an initialization rule because no rising transition may occur after startup.

Transition and Override Verification

Monitor the physical DI, system on auto, A, and B on one time-aligned view where possible. Start with the DI false and verify A is false, B is true, and only Button-2 appears selected. Change the DI to true and verify the complete opposite state. Repeat the transition several times while watching for zero-selection or double-selection intervals.

Press both buttons manually with the DI in each state. Under level control, verify that the DI-authoritative state returns after the next logic update. Under transition control, verify that the manual state persists until the next DI transition. Cycle power or restart the runtime with the DI in both positions and confirm that initialization produces the intended pair.

Finally, disconnect or interrupt the HMI communication path during a controlled test. The controller state should remain deterministic, and the display should report loss of current feedback rather than presenting a stale selection as confirmed.

Recurring Implementation Pitfalls

The most common fault is implementing the DI as a continuous assignment while expecting manual commands to persist. That requirement is contradictory until a priority or edge-trigger rule is selected. Another common fault is tying color or selection animation to an internal button bit instead of the controlled signals.

Separate SET and RESET operations in different routines also create order-dependent behavior. Search every task, screen event, macro, and controller routine that writes A or B. Multiple writers can make a correct local configuration appear intermittent.

Input chatter can produce repeated transitions in an edge-driven design. Diagnose it at the physical input and input image before changing screen logic. Read the input module’s filtering configuration and measure the field signal; select filtering from the actual noise and required response rather than entering an assumed timing value.

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