Sixteen binary digits on one line have no labels, so technicians count character positions and guess. Build the diagnostic page as a 4 by 4 grid of labeled indicator objects, with inputs and outputs on separate pages, and verify every bit against the controller before anyone trusts the screen. The one-line string remains for character displays, where a rotating labeled message beats a bare binary string.
You can put all 16 input or output bits on one screen page, and on most graphical editors the right answer is a 4 by 4 grid of labeled indicators, one object per bit, with the bit 0 corner marked on the page. The one-line binary string fits too: a digit is one character, so 16 bits take 16 characters. A line has no room for a label per point, so the technician counts positions, and one miscount reads the wrong point. Below is the arithmetic for both layouts, the build steps, a sizing example, and the verification walk that makes the page trustworthy.
One line or a grid
The one-line format is a capacity question. Sixteen binary digits need 16 characters. A space between each group of four brings the string to 19 characters. Character LCD modules come in 16- and 20-character line widths, so the digits fill a 16-character line exactly, with nothing left over, or fit a 20-character line with three separator spaces and one spare position. That is all a line holds: no point names, no headings.
A grid trades line width for area: one indicator object per bit, each with its own label, all 16 states visible at once. Every graphical editor draws this.
| Layout | Capacity | Labels | Use it when |
|---|---|---|---|
| One binary string | 16 digits, 19 with separators | none | text-only LCD, quick glance |
| Cycling labeled message | 1 bit at a time, about 30 s per full sweep | full | text-only LCD, point-by-point inspection |
| 4 by 4 indicator grid | all 16 at once | one per point | any graphical editor |
The grid is the default. Keep the string and the cycling message for panels with no graphics.
What you need
- The controller's I/O assignment: address and a short description for each of the 16 points. In slot-and-bit style notation an input reads I:1/0, slot 1, bit 0; your controller's own format governs.
- The editor's indicator light object, called a bit lamp in some editors, with a configurable on color and off color.
- Two colors that stay distinct under the panel's lighting, plus state text on the object where the editor offers it.
- A safe-state plan: which device you actuate, in which machine state, to toggle each of the 16 points.
- A return path off the page: a back button, or the screen-select register the PLC already writes.
Build the page
- Split the groups. Build one page for the 16 inputs and one for the 16 outputs. Thirty-two objects on one page doubles the build time and the polled points.
- Draw the 4 by 4 grid and mark the convention. Decide which corner is bit 0 and print it on the page, for example 'bit 0: top left'. One row per nibble keeps the mapping readable as a word.
- Create the first indicator object. Bind it to the address from the I/O assignment, set the label, set the on and off colors. When you later need a middle state such as tripped, healthy and fault, one indicator object can carry three states: see show three alarm states with one HMI indicator.
- Copy the object fifteen times where the editor supports it and change only the address and label on each copy. Where copying is missing, create each object fresh. That one-by-one work is the time cost of the page.
- Add the title and the return control. If the PLC switches to this page through a screen-select register, the register value has to change for the switch to fire again; PLC to panel screen switch register: retrigger the same screen covers the retrigger.
- On a text-only LCD, build the cycling message layout. One message per bit, each showing the point label and its state, on a timer of about 2 s per message, so a full 16-bit sweep takes about half a minute.
- Save the project and close the editor. Persistence is tested in the final checks below.
Example: sixteen inputs on a 4 by 4 grid
Scenario: a packaging line, 16 input points from guard switches, photo-eyes and drive fault relays, page read from 3 ft at the panel door.
Page area. Assume a 16:9 page of about 345 x 194 mm, the active area of a mid-size panel. Cells of 70 x 30 mm give 4 x 70 = 280 mm of columns, leaving 65 mm of margin on the 345 mm width, and 4 x 30 = 120 mm of rows, leaving 74 mm for the title line and the back button on the 194 mm height.
Text size. The FHWA legibility planning figure is 30 ft of viewing distance per inch of capital height, and 20 ft per inch is the safer choice for fast reading. At 3 ft, fast reading needs 3 / 20 = 0.15 in of capitals, about 4 mm. An average uppercase character runs about 0.7 of the cap height, so a five-character label is 5 x 2.8 = 14 mm wide, well inside the 70 mm cell. With the 1.7 x line spacing rule the label occupies about 7 mm of the 30 mm cell height; the rest holds the indicator shape.
Time. At a planning pace of 2 minutes per object for address, label and colors, the 16 objects take about half an hour. Copying an object, where the editor supports it, cuts the second through the sixteenth to seconds each. The verification walk, 16 toggles at about 30 s each, is an 8 to 10 minute job.
Result: all 16 states labeled and visible at once, and nobody counting character positions.
Verify every bit against the controller
Walk the inputs one at a time: machine in a safe state, actuate each device through its normal operation, confirm the bit moves in the controller's diagnostics, and confirm the matching object follows. Then walk the outputs: command each one from the PLC logic in a safe state. Do not force bits, and do not bypass an interlock to manufacture a test state.
Check bit order on the one-line and cycling layouts by setting one known bit in a staging register and watching which character or message changes. Confirm the sweep passes all 16 points, skipping and duplicating none.
If an object disagrees with the controller, stop using the page for troubleshooting and recheck in this order: the tag address against the I/O assignment, the bit order, the data type, the communication status. A page can look finished and still be bound to the wrong word.
An indicator page diagnoses. It never clears a machine for hands-on work: zero-energy verification stays with the lockout procedure, tested at the energy source.
How to check it worked
- Power-cycle the panel and reopen the page. All 16 objects, labels and tags should survive; if the panel drops its project after a power cycle, fix that before a shift relies on the page: HMI panel loses its project after a power cycle.
- Run one machine cycle you know well. Name the expected states first, then watch the grid match them.
- Test the return path both ways: onto the page and back to the main page.
- Watch the update rate with the page open. Sixteen objects are sixteen polled points, and on a controller already serving several panels that load adds up; connecting many operator panels to one PLC without slow updates covers where pages start to lag.
The decision
The panel doing this job is your HMI, with its own editor and driver; the page lives in that editor. If you also want a separate board beside the machine for andon counts or shift notices, that is a different screen doing a different job. Our shop-floor displays are Android all-in-one screens built for notice and status pages; they are not HMIs.
Recommendation: build one page per group, 16 labeled indicator objects in a 4 by 4 grid with the bit 0 corner printed on the page, keep the one-line binary string for text-only LCDs where no grid can be drawn, and walk all 16 bits against the controller before the first shift relies on the page, then again after any change to tags or addresses.
Questions
Can I put 16 inputs and 16 outputs on the same page?
You can, but label and separate the two blocks so no state is read against the wrong heading. Thirty-two indicator objects double the polled points and the build time, so most shops build two pages, inputs first. If one page is required, keep inputs in the upper block and outputs in the lower block under their own titles, and walk the two groups separately during verification.
One indicator stays on after I rewired a point. What do I check first?
Check the tag address before the screen. Deleting and redrawing the object leaves the address as it is: compare the tag with the controller's I/O assignment for that point, then actuate the device and watch the bit move in controller diagnostics. If the controller bit moves and the object still disagrees, check the driver's data type and bit order next. Do not troubleshoot field wiring from a page that has not passed its verification walk.
What text height do the labels need when the page is read from 6 ft?
Use the fast-reading planning figure of 20 ft of viewing distance per inch of capital height. At 6 ft that is 6 / 20 = 0.3 in of capitals, twice the 0.15 in a 3 ft viewing distance needs. A five-character label at that size needs about 1 in of cell width, so widen the cells or shorten the labels before you shrink the text.
Does the cycling one-bit message give a true snapshot?
No. A cycling message shows one bit's label and state at a time, and the state can change between one message and the next, so a short pulse can be over before its message appears. Treat the cycling view as point-by-point inspection and use the grid page when the technician needs all 16 states together.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.