Assign HMI function keys to four numeric entries on one screen

What you need

• The HMI project open in its programming software, with the screen that shows the four values.
• The four PLC data point addresses behind those values. In this setup the panel talks to a C0-01AR-D CLICK PLC over Port 2.
• Five function keys in use, F1 to F5, with F5 already toggling to the next screen.
• The simulator in the programming software, so you can test the keys with the PLC out of the picture. Plan 15 minutes in it before you touch the live panel.

Put one Numeric Entry object on each value

1. Add a Numeric Entry object to the screen for the first value.
2. Open the object's properties and point it at that value's PLC data point.
3. In the Numeric Entry set-up menu, on the left below Frame Style, assign the object F1.
4. Repeat for the other three values, with F2, F3 and F4.
5. Walk the four objects one by one and confirm each one writes to a different data point.

The key is what selects the value: pressing the key assigned to an object activates that object's adjustment menu. Give each object its own key, or the one-key-one-value certainty is gone. While you are on this screen, check the numbers read at the working distance. The common planning figure is 30 ft of viewing distance per inch of letter height, so values read from 6 ft want capitals of at least 0.2 in. The layout lands like this:

Set Object Style 2 on each object

The key assignment and the object style are two separate settings. The style is the one that turns the key press into an edit.

1. Select the first Numeric Entry object and open the Numeric Entry set-up menu.
2. On the bottom right of that menu, in Object Style, choose 2. This style uses the function keys for editing the value.
3. Confirm the function-key assignment on the left is still the key you set.
4. Repeat on the other three objects and save the project.
5. In the simulator, press F1 through F4 one at a time and confirm each key opens the adjustment menu for its own value.

If your operators will type the new value on a pop-up keypad driven by the keys, non-touch numeric entry with keypad style 2 covers that side of the setup.

Keep F5 on the screen change

Leave the screen change on F5 and keep F1 to F4 for the four entries. Two kinds of assignment can claim a key number: the per-object assignment you just made, and the screen-level function key assignment that changes screens. When a press does the wrong job, one of those two claims sits on the wrong key. Function key screen navigation covers the screen-level side. Test both directions in the simulator: F1 through F4 open menus, F5 changes the screen, and nothing does both.

Shared Up and Down keys: a pointer and a scratch pad

Some interfaces must keep one Up key and one Down key for whichever value is selected. Build that in the PLC:

1. Add a pointer tag to the PLC project that names which of the four data points is selected.
2. Add a scratch-pad tag that holds the value being adjusted.
3. Let F1 raise the scratch pad and F2 lower it.
4. Add ladder logic that copies the scratch pad into the data point the pointer names.
5. Give the pointer its own way to step through the four points, from a spare key or an on-screen selection.

This is the same indexed idea as saving each numeric entry to the next word of an indexed PLC table, with the pointer choosing the word. Every edit runs through the PLC copy before it lands, so test that the delay feels right to the operators. A copy that lands within one PLC scan of about 10 ms feels instant; a slower one does not. The scratch pad can stay off screen, but showing it while a point is selected keeps the operator from editing blind. Enforce the working range of every value on the PLC side; enforcing increment and decrement limits in PLC logic shows the ladder pattern.

Example: a filler panel with four setpoints and five keys

Picture a filling machine whose HMI screen shows four adjustable setpoints. The operator stands 6 ft from the panel, so the capitals for each value need at least 0.2 in of letter height to read clearly. The panel has five function keys in use, F1 to F5. F5 is reserved for the screen change. The old scheme used one Up key plus one Down key per value, which is 2 keys per value.

The rule in words: paired increment and decrement takes 2 keys per value, a Numeric Entry object with its own key takes 1 key per value, and the screen change takes 1 key.

The arithmetic, in keys on the panel:

• Old screen, two values: 2 values x 2 keys per value = 4 keys, plus 1 key for F5 = 5 keys. The 5 keys in use were exactly full, which is why it worked.
• Four setpoints, paired keys: 4 values x 2 keys per value = 8 keys, plus 1 key for navigation = 9 keys. The panel has 5 keys in use, short by 4 keys.
• Four setpoints, one key each: 4 values x 1 key per value = 4 keys on F1 to F4, plus 1 key for F5 = 5 keys. Full again, with nothing spare.

The result: at four values, one key per value is the only one of the two schemes that fits with navigation kept on F5.

Recommendation: Use one Numeric Entry object per value on F1 to F4 with Object Style 2, and keep F5 on the screen change, whenever the panel has a spare key for every value. Above four editable values the five keys in use run out. At five values, either move one to a second screen or switch to the shared Up and Down scheme, which serves any number of points with F1, F2 and a selection step.

How to check it worked

Run these with the PLC connected and the machine in a state where test writes are safe. The five checks below take about 10 minutes on the floor:

1. Record the four values as the HMI shows them and as the PLC holds them. They should match before you start.
2. Press F1, change the first value through its adjustment menu, and confirm the matching data point moved.
3. Confirm the other three points did not move. Four keys, four checks, one point moved each time.
4. Repeat for F2, F3 and F4.
5. Press F5, confirm the next screen opens, come back, and confirm the four values still match the PLC.

If a key opens the wrong value, that object's data point assignment is wrong. If a key opens nothing, recheck its function-key assignment and its Object Style 2 in the set-up menu. If a press changes the screen when it should open a menu, a screen-level assignment holds that key number; clear it and retest.

When the same numbers also matter to people who never touch the HMI, post the standing targets and instructions on a separate shop-floor notice screen beside the panel. Leave the live values on the HMI where the keys are.

Questions