One word register can show only one bitmap at a time because it holds one value. To show several images together, stack one bitmap object per image in the same screen area and drive each object's visibility from its own discrete tag. Keep the word selector for mutually exclusive images.
A word selector can never show two of its images at once. The register in this setup, V2001, is a 16-bit word, and the panel draws the image assigned to the value the word holds right now. Write 1, then 2, then 3 on three rungs and the panel shows the image for 3, because 3 is the value left in the word. The fix is not to convert the word into a discrete bit. Place one bitmap object per image in the same screen area and give each object its own discrete visibility tag. Two or three images then appear together whenever their tags are on, and the selector keeps the exclusive job it does well.
Why one word shows one image
A selector object reads the current value of its register and draws the image mapped to that value. A 16-bit word holds one of 65,536 values (2^16), but only one at a time. Assigning images at 1, 2 and 3 therefore makes them alternatives, never a group, and a scan that writes 1, 2 and 3 in sequence leaves the panel showing the last one. This is the same one-value-at-a-time rule that lets a single integer tag drive several color states from one tag, and it is exactly what you want when the states are exclusive, such as three alarm states on one indicator.
The wrong lever is forcing the word into a discrete. A selector picks one of several images; a visibility tag switches one object on and off. This screen needs the second job, applied once per image. Loading more bitmap files changes nothing either: the panel is showing the state of the last value the PLC wrote, the same way it follows the register behind a PLC-driven screen switch.
What you need
- One bitmap file per visual element. Your own artwork imports fine; check the programming software's help for the file formats, color depths and pixel sizes it accepts.
- A transparent background on every overlay image, wherever the layer underneath must stay visible.
- One bitmap object per image on the screen.
- One discrete tag per independently shown image: a real coil or control bit in the PLC whose on state means this element should be visible now.
- A saved copy of the current project before you edit anything.
Stack the bitmaps and set each visibility tag
- Split the artwork. If a base drawing and two banners must appear in combinations, make one file for the base and one file per banner. Import each file and confirm it renders in the editor before you wire any tags.
- Place the base bitmap object first, in the screen area the graphic occupies.
- Place each overlay as its own bitmap object at the same position and size, aligned to a shared reference point. Draw order matters: a later opaque object covers an earlier one, so the base goes in first and the overlays stack on top.
- On each overlay, enable visibility. Every HMI package words it slightly differently, but the control is the same: a visibility option on the object that takes a tag name and a condition, such as visible while the bit is on.
- Point each visibility tag at a real bit the PLC project declares. Do not reuse V2001 for these objects, and do not type an address the PLC has not defined.
- Save the project and download it to the panel under your normal change-control process.
Example: one word, three images, four display states
A packaging machine needs a status tile of 400 × 300 pixels in the corner of an HMI screen: a machine drawing of 400 × 240 pixels that is drawn in every state, a fault banner of 400 × 60 pixels, and a door-open banner of 400 × 60 pixels, where fault and open door can be true together.
The current screen maps three bitmap objects to V2001, with the drawing at 1, the fault banner at 2 and the door-open banner at 3. A fault with the door open writes 2 and then 3, so the tile shows only the door-open banner. The tile can show 1 image from its list; the machine needs 4 display states: drawing only, drawing plus fault, drawing plus door, drawing plus both.
Split it into three objects. The drawing keeps no visibility condition, so it draws in every state. The fault banner gets visibility bit F and the door-open banner gets visibility bit D. Two bits give 2 × 2 = 4 combinations, exactly the 4 states the machine needs:
| F | D | The tile shows |
|---|---|---|
| 0 | 0 | drawing |
| 1 | 0 | drawing and fault banner |
| 0 | 1 | drawing and door-open banner |
| 1 | 1 | all three |
A fourth overlay would make it 2^3 = 8 combinations, still one bit per object.
Recommendation: keep V2001 with its 1, 2, 3 image assignments only where exactly one image may show at any time. Where two or more images must appear together, place one bitmap object per image in the same screen area, enable each object's visibility option, and drive each from its own discrete bit, as in the example above.
How to check it worked
- Force each bit on alone and confirm its object appears while every other object stays as designed.
- Force both bits on and confirm both overlays draw, aligned, with no opaque layer hiding a required element.
- Turn each bit off and confirm its object disappears.
- Compare the panel with the PLC values online, on the target panel and not only in the editor preview.
- Watch for order dependence: if an image appears only after a particular rung fires last, one of the objects is still mapped to the word.
- If a non-static (animated) bitmap misbehaves after the tags check out, run the same layout with a static image. Some panels have had quirks with non-static bitmaps; the documentation for your software version is the record of what was fixed, and the static swap separates a configuration problem from a graphics problem fast.
Selector or separate bits: the decision
| Display job | Wiring |
|---|---|
| Exactly one of several images at any time | Keep the selector: one register, one image per value |
| Two or more images can be true together | Separate objects in one screen area, one visibility tag each |
| One image must hide while a condition holds | A visibility condition on that single object |
| Combinations must arrive over one register | Keep the register as the source and decode its value to bits in the PLC |
The HMI panel and its project stay the right tool for machine bitmaps. An Android signage display is the wrong choice here: it takes no video input and reads no PLC registers. When the same line also wants a separate screen for shift notices, targets and safety messages, that is a notice board with its own job, and our shop-floor signage displays are built to play their content offline from a card.
Questions
Can I keep the word register and still show combinations?
Yes, if the register itself encodes the combinations. Keep V2001 as the source, write combination values into it from the PLC (0 for drawing only, 1 for drawing plus fault, 2 for drawing plus door open, 3 for both overlays), and decode each value to a discrete bit with a compare rung. Each stacked object then uses its decoded bit as its visibility tag. The selector object with one image per value still cannot do this, because it can only draw the image for the value it currently holds.
Where do the bitmap images come from?
You can make your own with any graphics tool, and the programming software ships libraries of ready-made graphics. Before you design, check the software's help for the file formats, color depth and pixel sizes it imports. Keep a transparent background wherever a lower layer must stay visible. If an import is rejected, convert the image to a format the help lists and import the converted copy.
How many bitmaps can I stack this way?
The method sets no count: one bitmap object per image and one visibility tag per object. The real limits are the screen area the stack covers and the project memory of the panel, which the programming software reports when it builds or downloads the project. Keep each image sized to the area it covers, and give anything that does not need to share that area its own object elsewhere on the screen.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.