Tags and Addresses

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License feature: Ladder Logic

Every operand — a contact's Tag, a compare's Source A, a math block's Destination — has a source type chosen from a drop-down.

Type	What it is	Read	Write
Device Tag	A tag on any device, including Local Tags. Click Browse to pick it; the box then shows Device #3 / Line1/Speed	The value at the start of the scan	Collected and written after the scan (see below)
Task Tag	Internal memory shared by every program in this task	Immediately	Immediately
Program Tag	Internal memory private to this program	Immediately	Immediately
Literal	A constant typed in the box (Constant value), e.g. 450, 2.5, 1	Always that value	Cannot be written

A new contact or coil starts as Device Tag with Not set. An operand left unset reads as 0 / false and writes nowhere.

Task Tag and Program Tag addresses

Type an address in the box (e.g. B3:0/0, N7:0, F8:0). The first letter(s) decide the type; the rest is just a name, so you can use Allen-Bradley style addresses or readable names:

Starts with	Type	Examples	Stored as
B	Bit	B3:0/0, B_Motor_Run	on/off; writing 1 or true sets it
N	Integer	N7:0, N_PartCount	whole number — writes are rounded
F	Float	F8:0, F_TempC	decimal number
ST	String	ST9:0, ST_Recipe	text (only DTOS writes text)
Tn:n	Timer	T4:0, T4:0/DN, T4:0.ACC	a timer given that address (see below)
Cn:n	Counter	C5:0, C5:0/DN, C5:0.ACC	a counter given that address
anything else	—	Count, Temp	not stored — reads give 0

Warning: Apart from timer and counter addresses, only the first letter counts: a name like Flow is a float, Batch is a bit, and Count is ignored.

Timer and counter addresses

Give a TON, TOF, RTO, CTU or CTD an Address (a Task or Program Tag such as T4:0 or C5:0) and other elements can use its members:

Member	Timer	Counter	Writable
/DN (or the bare address)	done	done	no
/TT	timing	—	no
/EN	rung power into the timer	—	no
/CU, /CD	—	rung power into the counter	no
.ACC	accumulated milliseconds	count	yes
.PRE	preset (ms)	preset	yes — replaces the element's Preset; the written value is kept across Save, Stop/Run and restarts until written again

• RES clears the addressed timer or counter.
• Elements with the same address share one timer or counter, as on a PLC.
• A Task Tag address is shared by all programs in the task; a Program Tag address is private to the program.

Internal tags are not visible outside the task: you can't show them on a dashboard or use them in a workflow. They start at 0 (or empty), and are saved every 10 s and when the task stops. Copy a value to a Local Tags tag when something else needs it.

How values are read

• Contacts (XIC, XIO, OSR, OSF) treat true and 1 as on, false and 0 as off, any other number as on if it is not 0, and any other text as off.
• Numeric operands convert the value to a number; text that isn't a number becomes 0.
• Coils write 1 and 0, not true/false.

Where device-tag writes go

Device	What happens
Local Tags	The tag is updated when the value changes; dashboards, workflows, scripts and alarms see it
Simulator	The simulated value is updated when it changes
A real device (PLC, robot, drive…)	The driver writes the device when the value changes. If the device still reads a different value two seconds later — another HMI changed it, or a write was lost — it is written again. It is never written every scan

• The device needs Tag Write Access turned on (device settings). If it is off, nothing is sent and the task log gets a write_error entry naming the tag and device, at most once a minute per output.
• A failed write (device offline, driver refused it) is logged the same way; the next change is sent as usual.
• Writes are not permission-checked per user: the task acts as the system.

Examples

Element	Setting
XIC	Tag: Device Tag Conveyor PLC Conveyor_Running — passes power while the conveyor runs
GRT	Source A: Device Tag Furnace/Temp; Source B: Literal 450
MOV	Source: Literal 0; Destination: Program Tag N_RecipeStep
OTE	Tag: Device Tag Local Tags Line1/Ready — for the HMI

See also

• The Scan Cycle
• Element Reference: Bits, Timers, Counters, Compare
• Tags & the Tag Browser
• Devices
• Local Tags
• Cookbook: Conveyor Start Interlock in Ladder Logic