Tags

A tag is a name for one robot signal. Instead of every control referring to DO[5], you declare a tag called clamp_closed once and controls refer to that.

When a signal moves to a different address, changing the tag updates every control that refers to it.

Tags live in the document, so a document carries its own bindings — export it, import it on another controller, and the names come with it.

Signal kinds

Kind	What it is	Direction
DI / DO	Digital input / output	read / write
RI / RO	Robot input / output	read / write
AI / AO	Analog input / output	read / write
GI / GO	Group input / output	read / write
F	Flag	write
R	Numeric register	write
SR	String register	write
TIMER	TP timer, in seconds	read
LPOS	Cartesian position component — X, Y, Z, W, P, R	read
JPOS	Joint position component — J1 to J6	read
SYS	A system value from a fixed list. See System values.	mixed
KAREL	A variable inside a KAREL program, by program and variable name. See KAREL variables.	read / write
LOCAL	A scratch value that lives only in the HMI and never reaches the controller	write

Adding tags

1. Open the Tags panel and press + Add tag.
2. Choose the kind and index — DO and 5 for DO[5].
3. Give it a name. A new tag is named after its signal (DO[5] becomes do_5) so it is never nameless; rename it to what the signal does.

Names are what labels interpolate and what expressions reference.

What a name may contain

Letters, digits and underscores, starting with a letter or an underscore: part_present, do_5, Cycle2.

Spaces, &, - and other punctuation are not accepted. A name has to be usable as {name} in label text, and a name with a space in it cannot be — the placeholder would appear on the screen exactly as written.

A document written before this rule can still contain such a name. It keeps working for bindings, and the Validation panel reports it.

KAREL variables

A KAREL tag reads and writes a variable inside a KAREL program. Instead of an index it takes three things:

1. Program — the KAREL program that owns the variable.
2. Variable — the variable’s name.
3. Type — INT, REAL or STRING. The tag’s declaration decides how the variable is read and written, so it must match the declaration in the KAREL source.

With a controller connected, both fields are pickers — the programs and their variables are listed, and picking a variable fills in its type. Type a name… switches to a text field for an array element or structure field, or when authoring away from the cell.

Both names use letters, digits and underscores, starting with a letter or an underscore. The variable must be declared at program level in the KAREL program — a routine-local variable cannot be reached. The variable is a path: an array element by its subscript (byteval[1]) and structure fields by dots (struct.array[1].foo[2].bar), as long as the value at the end of the path is an INT, REAL or STRING. A whole array or structure cannot be read, and a multi-dimensional subscript ([1,2]) is not supported. INT tags also read SHORT and BYTE variables; the controller wraps an out-of-range write to them silently (256 into a BYTE becomes 0), so Validation flags a button value outside the variable’s range.

A tag whose program is not loaded on the controller, or whose variable does not exist or has never been assigned, reads as no value — controls show their empty state. When the editor is connected to the controller, the Validation panel checks each KAREL tag against it and reports a missing program, a missing variable, or a declared type that does not match the variable’s real one.

A STRING value written from a screen cannot contain &, %, +, =, ; or characters outside ASCII, and is limited to 200 characters. A value longer than the variable’s declared length is silently cut short — the controller reports no error — so declare a STRING variable the screen writes to at least as long as anything it will be sent; STRING[254] makes that impossible to hit. Validation also checks a button’s literal value against the variable: a value that is not a number cannot be sent to an INT or REAL, and text longer than the variable’s declared length is flagged before it ever runs.

Using a tag

Bind a control to a tag in its Inspector, reference it in an expression as {tag_name}, or interpolate it into a label the same way. The Tag button beside label and expression fields inserts the braces for you — on the pendant keyboard they are two pages deep.

A read-only kind cannot be a write target: the tag pickers for a slider, a number input or a button’s write action only offer tags that can actually be written.

Related

• Expressions — using tags in conditions.
• System values — controller values usable by name, with no tag to declare.
• USB import & export — moving tags between documents.