Move an HMI numeric entry into PLC memory on Enter

What the panel does when you press Enter

The manual for this class of two-line, 20-character operator panel documents a four-step cycle for numeric entry:

1. The operator types digits on the numeric keypad and they show on the entry line. Nothing has reached the PLC.
2. Enter. The panel writes the value into the entry register assigned to the entry module, V2000 in this configuration, and sets the DA bit in its status register. The manual documents this bit as the signal to the PLC program that data has been entered.
3. Your rung moves V2000 into your application register. This is the step your program owns, and the step that is missing when messages work and numbers do not.
4. Your rung sets the Data Acknowledge bit. The panel clears DA and allows new data entry, and the manual requires the acknowledge bit cleared once DA has dropped.

Three jobs, three owners: the message prompts the operator, the panel reports a completed entry, the PLC copies it. The prompt never does the copy. The arrow keys only navigate the display; Enter starts the handoff because it is the key press that sets DA.

Symptoms and what each one points to

• The prompt shows, the arrow keys navigate, the application value never moves. The display path is healthy and no rung is taking the entry. Add the rung below.
• V2000 shows 12 after Enter but your register stays put. The move rung is missing, never enabled, aimed at the wrong destination, or overwritten a scan later. Monitor both registers across one Enter and the failing step shows itself.
• The first entry lands and the second does nothing. DA is still set. The panel holds new entries until the Data Acknowledge bit clears DA, so finish step 4 of the cycle.
• Your register takes 12, then drifts back to the old value. A second rung is writing the destination. Cross-reference the destination address in your programming software.

Check the entry path before editing the machine logic

1. Put the machine where a changed register can do no harm: outputs disabled or the machine out of cycle. The value you are about to move lands in a register the machine logic reads.
2. Show the entry message, type 12, press Enter.
3. Watch V2000 and the DA bit. Expected result: V2000 = 12 and DA = 1.
4. If V2000 never takes the value, stop at the panel. The entry register assignment lives in the panel's configuration software, and the mapping to verify is between the entry module and its V-memory address. If the address refuses to tag at all, work through fixing HMI invalid address errors when tagging PLC memory before going further.

The rung: one move on DA, then the acknowledge

Build it from five elements:

1. A contact on the DA bit from the panel's status register.
2. A one-shot on that contact, so one Enter produces one move.
3. A move instruction with source V2000 and your application register as destination.
4. A SET of the Data Acknowledge bit on the same one-shot.
5. A RESET of the acknowledge bit driven by a normally closed DA contact, so it drops after the panel clears DA.

In structured text, with the panel's documented names and yours separated:

Entry_DA    : BOOL            // documented: the DA bit in the panel status register
Ack         : BOOL := FALSE   // documented: the Data Acknowledge bit
Entry_Reg   : INT             // documented: the entry register, V2000 in this configuration
Preset_Dest : INT := 8        // yours: the application register this example writes

IF rising_edge(Entry_DA) THEN
    Preset_Dest := Entry_Reg;  // the move
    Ack := TRUE;               // answer the panel
END_IF;
IF NOT Entry_DA THEN
    Ack := FALSE;              // required once DA has dropped
END_IF;

That is the pattern; substitute the two documented bits and the register from your own configuration printout. Two additions are worth making while you are in the ladder: a range check on the moved value, and the correct wiring when the destination is a counter preset. Clamping HMI numeric entry limits in PLC ladder logic covers the range check, and loading counter presets from an HMI into a counter module covers the counter case.

Worked example: entering 12 into a timer preset

The application register Preset_Dest holds 8 and feeds a timer with a 0.1 s time base, so the machine currently runs 8 x 0.1 s = 0.8 s. The operator types 12 and presses Enter.

Step 2 is the fix: 12 replaces 8 in Preset_Dest, and with the 0.1 s base the timer runs 12 x 0.1 s = 1.2 s. Step 5 is the proof: a second, different value through the same path rules out a stale register or a display-only change. If step 1 leaves V2000 at 0, the fault is upstream in the panel configuration. If step 2 leaves Preset_Dest at 8, the fault is the rung.

If the setpoint also needs an audience

The keypad stays the input device. When the entered setpoint also has to be readable across the floor, that becomes a one-way display decision: live factory data display, signage or dashboard walks the choice, and shop-floor screens playing content from a card cover the read-only case.

Recommendation: wire the move to the rising edge of DA from entry register V2000, finish the handshake with the Data Acknowledge bit, and prove the path with entries of 12 then 47 while the machine outputs are disabled. Only then return the terminal to the machine.

Questions