NEQ — Not Equal

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Description

NEQ (Not Equal) is true when Source A and Source B differ. It is the inverse of EQU and, like it, a condition that writes nothing. Use NEQ to detect a mismatch: a feedback value that has not caught up with a command, a mode word that is anything but idle, a checksum that does not match. Do not use NEQ to detect a change over time; it compares two values on the same scan, not one value against its previous scan.

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Operands

Operand	Type	Format	Valid Range	Required	Description
Source A	Any numeric tag, member, element or bit; a STRING tag; or a literal	Tag, Tag.Member, Tag[n], Tag.bit, or a literal	Any resolvable reference	Yes	The first value.
Source B	Same as Source A	Same	Any resolvable reference; defaults to 0	Yes	The value to compare against.

Literals may be whole numbers (25, -3, 0x1F), decimals (72.5), or quoted strings ("RUN"). A BOOL reads as 0 or 1. STRING operands compare by content, case-sensitively.

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Scan Behavior

Prescan

No state. Evaluates from the current values on the first scan.

Rung-condition-in is false

The instruction does not pass continuity. The block still colours by its own result on the canvas.

Rung-condition-in is true

Both operands are read. If they differ the instruction conducts; if they are equal the rung is false from this point.

Postscan

Nothing.

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Example

Scenario: A stepper sequence is commanded to a step number and reports the step it is actually on. While the two differ, the sequence is in motion and a “busy” lamp is lit.

Tags:

• Cmd_Step — Commanded step, INT
• Actual_Step — Reported step, INT
• Busy — Busy lamp, BOOL

Rung 1:

—[NEQ Actual_Step  Cmd_Step]———(OTE Busy)———

Scan 1 — both read 3. The sequence is parked on the step it was sent to. The values match: the block is dark, the rung is false, Busy = 0. Both operands are tags, so each shows its live value beneath it.

Scan 2 — Actual_Step reads 0. The sequence has been reset to home while Cmd_Step still calls for step 3. 0 is not 3: the block lights, the rung is true, Busy = 1, and it stays lit until Actual_Step climbs back to 3.

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See Also

• EQU — Equal (the inverse test)
• CMP — Compare by expression
• XIO — Examine If Open (the same idea for a single bit)
• Compare Instructions — Category index

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Notes

NEQ against zero. NEQ Word 0 is true when any bit of Word is set, a quick “anything active?” test on a status word.

REAL values. Two REALs that were computed separately will almost always be “not equal” by a rounding error. Compare REALs with LIM, or with a GRT on the absolute difference from CPT.

Not a change detector. To act once when a value changes, keep a copy with MOV and compare against the copy, or use an ONS on the NEQ result.