Set HMI tab order for arrow key numeric entry

How do arrow keys select a numeric entry field on a non-touch HMI?

The arrow keys move the selection from object to object in Tab Index order, Enter opens that object's numeric keypad on the screen, and the bezel keys type the digits, so tab order decides which field an operator reaches next.

A touch panel replaces all of this with a tap on the object. The non-touch bezel does the same job with two keys: the arrows step the selection along the cursor path, and Enter commits the choice. The cursor path runs through the objects on the screen, entry fields and indicators alike, in Tab Index sequence, so the position of every entry field in that sequence is a setting you control. When the operator presses Enter and the wrong object answers, that is a tab order problem, and the fix lives in the object settings, never in the ladder.

Tab order sets the path from field to field within one screen. Moving between whole screens is a different setting, covered in fixing HMI function key screen navigation across screens.

Where is the tab order setting for HMI objects?

Each object carries a Tab Index number, set under the Function Tab in the object's own settings, and the arrow keys follow those numbers, so the first field the operator fills gets 1 and each later field steps up by one.

You edit the number inside the entry object's configuration, the same place its register address and numeric format live. Number the fields the way the operator travels the screen, and include the objects the operator passes on the way, because the arrows cursor through the screen's objects, not only the entry fields. Give each entry field its own number, then prove the resulting path at the panel with the arrow keys before anyone keys a production value. The panel walk, not the numbering on paper, is the test that the order is right.

What do you need before you set the tab order?

You need the screen layout with its entry objects, the PLC register each object writes to, the entry length you plan for, 4 or 6 digits, and the PLC programming software open on its register monitor.

• The working order: which field the operator fills first, second and third on that screen.
• The register behind each field. In the example project below, the three fields write to V2000, V2001 and V2002, one 16-bit word each.
• The planned entry length, because a 4-digit value and a 6-digit value land in different register widths, as the register-size section explains.
• The numeric entry object's configured format and valid range, so a test entry has a defined place to land.
• The PLC programming software with its register monitor, set to decimal before the first test, so the write can be checked without converting in your head.

How do you set the tab order step by step?

Open each numeric entry object's settings, set its Tab Index under the Function Tab to its place in the operator's sequence, save the project, send it to the panel, and walk the order with the arrow keys before anyone keys a value.

1. Open the screen that holds the numeric entry objects.
2. Open the first field in the operator's sequence, find Tab Index under the Function Tab, and set it to 1.
3. Set Tab Index 2 on the next field, then 3, and so on through every entry object on the screen.
4. Give any object the operator passes on the way, such as an indicator, its place in the same sequence, so the arrows never have to step past clutter to reach the next field.
5. Save the project and send it to the panel.
6. At the panel, press the arrow keys and watch the selection travel the fields in the planned order. If a field comes up out of place, correct that object's Tab Index and resend.

Nothing in this sequence touches the PLC program. Tab order is panel-side project data, and the ladder only ever sees the registers the objects write.

How does an operator enter a number with the bezel keypad?

The operator arrows to the field, presses Enter to open the on-screen numeric keypad, keys the digits on the bezel, and presses Enter a second time; the confirmed value then lands in the register configured on the object.

The on-screen keypad takes the digits as they are keyed, so the operator sees the number build up before committing it. The first Enter selects and opens; the second Enter commits and writes. How that final Enter moves the value into PLC memory is its own step, and moving an HMI numeric entry into PLC memory on Enter covers it. If the keypad pops up cramped and hard to read on a high-resolution panel, fixing an HMI numeric keypad that is too small on a high-resolution panel is the companion fix.

Worked example: what lands in V2000 when the operator keys 1234?

Field one on the batch screen holds Tab Index 1 and writes to V2000; the operator keys 1234 and presses Enter, and the 16-bit word at V2000 reads 1234 in decimal, which a hexadecimal monitor prints as 04D2.

The screen is a packing bench project with three entry fields: batch quantity, target count and reject limit. Tab Index 1, 2 and 3 follow the operator's path, and the fields write to V2000, V2001 and V2002, each configured as unsigned decimal in one 16-bit word, with the monitor radix set to decimal.

The operator arrows to batch quantity, presses Enter, keys 1, 2, 3 and 4 on the bezel, and presses Enter again: the field shows 1234 and V2000 reads 1234. Enter lands the selection on target count; 2500 keyed and confirmed puts 2500 in V2001. Reject limit gets 150, and V2002 reads 150. Three writes, three matches.

With the monitor left in hexadecimal, the same three writes print as 04D2, 09C4 and 0096. The first conversion runs: 0x04D2 = (4 x 256) + (13 x 16) + 2 = 1024 + 208 + 2 = 1234. The other two check out the same way: 0x09C4 = 2304 + 192 + 4 = 2500, and 0x0096 = 144 + 6 = 150.

Why does the PLC monitor show 04D2 instead of 1234?

Because the PLC programming software's register monitor is printing the word in hexadecimal: 04D2 is 1234 in decimal, since 4 x 256 = 1024, 13 x 16 = 208, and 1024 + 208 + 2 = 1234.

The radix is a display choice. The register holds the same bits either way, so the write succeeded and only the printed characters differ. Set the monitor to decimal once and compare directly from then on, or convert each word before you compare it. Keep one base through the logic too: a compare against a constant must use the base the software expects at that field, because 04D2 and 1234 are the same value in two character sets.

A different symptom calls for a different fix. When the field reads far larger than the keyed value, the data format is the suspect, and setting the signed decimal data format when an entry reads as a huge number walks that one.

Will a 6 digit entry fit in one PLC register?

A 4-digit value fits one 16-bit register, because the largest unsigned 16-bit number is 65535 and 9999 is smaller; a 6-digit value up to 999999 does not fit, so set the object and the PLC logic to a 32-bit double-word format or scale the value down.

The arithmetic: one unsigned 16-bit word counts from 0 to 65535, and 999999 is roughly 15 times that ceiling. A 32-bit unsigned word counts to 4294967295, so a 6-digit entry fits with room to spare, provided the entry object's format and the PLC logic both use the 32-bit width. Scaling is the alternative: store the value in tens or hundreds and multiply in the ladder, which keeps the register 16-bit at the cost of resolution.

Whatever the width, set the object's predefined valid range to the largest value the process allows, and back it with a clamp in the ladder so the controller rejects an out-of-range key-in even if the panel-side range is set wrong: clamping HMI numeric entry limits in PLC ladder logic shows the rung.

What should you test before operators use the panel?

Walk the arrow keys through every field in the planned order, key a short value and the longest planned value into each, and confirm the panel field and the register monitor agree after Enter, at both 4 and 6 digits.

• Order: arrows through every entry field on the screen, front to back, with no field skipped and none visited twice.
• One write watched live: with the monitor on decimal, key a short value into the first field and confirm the field and its register agree after Enter.
• Mid-entry behavior: on setups like this, the monitored words can show values that reflect key presses before Enter; judge every write by the value present after the final Enter.
• Longest entry: 9999 in each 16-bit field, and the full 6-digit maximum only after the 32-bit format is in place on both the object and the logic.
• Logic side: the rung that consumes the value reads the same register, in the same width and base the entry writes.

If the cell also needs a notice or status screen standing apart from the HMI, that is a different job; we build shop-floor signage displays for it.

Recommendation: number the entry fields in operator order, Tab Index 1 for the first field and one step up per field, and prove the order and the write with a test entry before production. Keep 4-digit values in one 16-bit register, and move any 6-digit entry to a 32-bit format on both the object and the logic, because one unsigned 16-bit word tops out at 65535.

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