A tag screen asks for a name, a device, a data type and a PLC address. The name is a project label; the device is the link configured in Panel Manager; the address is the data in the controller. Set the device and the data type first, and the editor offers only valid addresses.
Three of the four fields on a tag screen do the connecting, and one is only a label. The tag name is the label: any name you like, best matched to a symbol in the PLC program. The device name is the communication link you configured in Panel Manager. The PLC address is the data itself, inside the controller. The data type decides which addresses are legal. Set them in that order, device, data type, address, name, and the editor hands you valid address choices instead of blank boxes. This page walks one push button tag from an empty project to a verified press.
What are the four fields on a tag screen asking for?
The tag name is a label you invent, the device name selects one configured communication link, the PLC address names the exact data in the controller, and the data type decides which addresses the editor will accept.
| Field | Where it lives | What it does |
|---|---|---|
| Tag Name | your HMI project | a label of your choice; matching a PLC symbol keeps the screen traceable to the rung |
| Device Name | the link configured in Panel Manager | picks the controller connection the tag uses |
| PLC address | the controller's data table | identifies the exact data the object reads or writes |
| Data type | the tag configuration | narrows the address list to values that fit the data |
Only the name is free text with no effect on the connection. A wrong name shows the right data under a misleading label. A wrong device or a wrong address moves the object onto different data while the screen still looks finished. Length is on your side: one published PLC naming convention allows tag names of 40 or more characters, so a descriptive name costs nothing.
Where does the device name come from?
Open the Function tab, then Panel Manager: the DF1 link to your PLC is assigned there to a device with a name like dEV001, and that exact name is what the tag's device field wants. The device is created when the communication link is configured, and the PLC type and protocol for it are set in the same place; set the PLC type in Panel Manager walks through that step.
Each configured link is its own device. A project with several controllers therefore offers several device names on every tag, which is how you point one HMI panel at multiple PLCs with per-device tags. Select the name your own project shows, never a name copied from an example.
Why pick the data type before the address?
The address field fills with valid possibilities only after the device name and the data type are set, so choosing them first turns address entry from typing into picking. Select the device, and the PLC address fields list only the possibilities valid for the tag's data type.
The stall that catches most first projects is an overloaded address box. The box wants one address, in the form the editor accepts, and nothing else: no data-file prefix, no symbol name, no comment. If an entry will not fit, the extra text is the problem, so remove it and pick from the list instead of trying another format. Length is rarely the limit: one engineering tool documents its tag address as a string of up to 128 characters, and a single address on a controller with a data table uses only a few of them.
Recommendation: Select the device and the data type first, take the PLC address from the choices the editor then lists, and enter the tag name last, matching a PLC symbol whenever you can export one.
How do you set a push button tag step by step?
Seven steps take a push button from a blank project to a working tag: confirm the device, insert the object, name the tag, select the device, set the data type, choose the address, then verify. You need the HMI project software on the computer, the PLC program open in its programming software, and the panel connected to the controller.
- Open the project and confirm the DF1 device for your PLC is present in Panel Manager, with the PLC type and protocol already set.
- Insert the push button object on the screen and open its tag configuration.
- Type the tag name. Any name works; a name matching a PLC symbol keeps the screen traceable.
- Select the device name Panel Manager shows, for instance
dEV001. - Set the data type to match the data the PLC program watches for that button; a start or stop command is normally a single bit.
- Choose the PLC address from the list the editor now offers for that device and data type. One address, nothing else in the box.
- Save, download the project to the panel, and verify the tag before you trust the button.
Can the PLC program's symbols become tag names?
Yes: export the symbol database from the PLC programming software with Tools > Database > ASCII Export, choose the CSV tab, and import the file so the tag names arrive ready-made in the HMI project. The export carries the symbol names you already assigned, and the import saves typing across a whole symbol set.
The import is a name service only. Every imported tag still needs its device selected and its address chosen, one tag at a time, because the binding lives in the device and address fields, and the exported file carries names.
How does an example push button tag come together?
A start command on one motor shows the whole binding: a 14-character tag name matched to a PLC symbol, the device dEV001, a single-bit data type, one address from the editor's list, and a verified 0-to-1 change in the controller.
Take a start command for a motor. The PLC program already carries the symbol Motor_Start_PB on the rung that seals in the starter, and the name is 14 characters, comfortably inside the 40 or more characters one published naming convention allows. Export it with Tools > Database > ASCII Export on the CSV tab and import the file, so the tag arrives already named Motor_Start_PB.
On the push button, set the device to dEV001, the data type to a single bit, and the address to the one the editor lists for that rung's bit. Press the button on the panel with the PLC data table open: the bit changes from 0 to 1, the rung executes, and the name on the screen matches the symbol in the logic. Four fields, one press, and the tag is verified against the controller before the machine depends on it.
How do you verify the tag against the running PLC?
Watch the data move in the controller while you work the screen: press the button and see the addressed bit change in the PLC data table, with the programming software open beside the panel. Download the project, put the data table for the addressed data on the screen, and operate the object.
For a push button, press and hold, read the bit, release, read it again, and confirm the rung that uses the bit does what you intended. For a display object, read the value on the panel and the same data in the table, and compare. A finished-looking screen can still point at data the PLC program never uses for that function, and this comparison is what catches it. Test the first press with the machine in a state where the commanded motion is safe, because the button now reaches real outputs. If a numeric display shows nothing at all on this first pass, treat the tag address as the first suspect and check the tag address first.
What if the object shows the wrong value?
Check the four fields against the PLC program one at a time, in the order device, data type, address, name, because each field fails differently and the order separates a binding error from a label error.
- Wrong device: the object reads a different configured connection, so its value tracks another controller or never moves.
- Wrong data type: the address was chosen for the wrong kind of data, so numbers read strangely; a BCD register read as plain binary is one such case, and nonsense numbers from a BCD analog register covers that fix.
- Wrong address: the value updates, but it belongs to different data in the controller. Hand-typed addresses cause this, as when a thumbwheel object receives a partial operand instead of the full one; write the full operand shows the pattern.
- Wrong name: the binding is right and only the label misleads. Rename it and leave the device and address alone.
Change one field, re-test, then move to the next. Three of the four mistakes are repaired in the tag editor; the fourth, a PLC program that ignores the data the object writes, is repaired in the logic.
Questions
Does the tag name have to match a symbol in the PLC?
No. The name is a label inside the HMI project, and any name works. Matching a PLC symbol pays off at maintenance time, because a technician can trace the screen value back to rung logic by name, and exporting the symbol database as CSV gives you the matched names ready to import.
How long can a tag name be?
Platforms differ, so check yours: one published PLC naming convention allows tag names of 40 or more characters, and one engineering tool documents tag address strings of up to 128 characters. A name short enough to read on the screen object serves you better than a long one.
Which object should hold a PID's information?
The loop runs in the PLC, and screen objects only display values or enter setpoints. Use the PID faceplate objects the editor provides for showing levels and settings, and point numeric entry objects at the setpoint and tuning values the PLC program exposes. Neither object is the control loop itself.
Why did the address field reject my entry?
The usual cause is extra information: a data-file prefix, a symbol name or a comment typed into a box that wants one address. Select the device and the data type first, then pick from the address choices the editor lists for that pair before typing anything by hand.
Planning information, not legal or engineering advice. Rules differ by place: check codes and permits with your local authority and your licensed trades.