DIV — Divide

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Description

DIV (Divide) writes Source A divided by Source B to Dest every scan its rung is true. It is an output instruction with no state and no status bits. Use DIV for an average, a rate, a ratio, or to split a total into equal parts. Do not use DIV when the divisor can be zero and Dest must change anyway; a zero divisor skips the write and Dest keeps its old value, so test the divisor first if that matters.

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Operands

Operand	Type	Format	Valid Range	Required	Description
Source A	Any numeric tag, member, element or bit, or a literal	Tag, Tag.Member, Tag[n], Tag.bit, or a literal	Any resolvable numeric reference	Yes	The dividend.
Source B	Same as Source A	Same	Any resolvable numeric reference; 0 skips the write	Yes	The divisor.
Dest	A writable numeric tag, member or element	Tag, Tag.Member, Tag[n]	SINT, INT, DINT or REAL; not a literal, not an input pin	Yes	Where the quotient is written.

Whole numbers and fractions. The type of Dest decides how the division is done:

Sources	Dest	Result
Both whole numbers	INT, SINT or DINT	Whole-number division, truncated toward zero: 7 ÷ 2 is 3, −7 ÷ 2 is −3.
Both whole numbers	REAL	Floating-point division: 7 ÷ 2 is 3.5.
Either a REAL	any	Floating-point division; a whole-number Dest then truncates toward zero.

There is no remainder output. To get one, multiply the truncated quotient back and subtract, or use CPT with TRN.

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Scan Behavior

Prescan

Nothing. Dest keeps its power-up value.

Rung-condition-in is false

The instruction does nothing. Dest holds its last value.

Rung-condition-in is true

Both sources are read. If Source B is not zero the quotient is written to Dest. If Source B is zero nothing is written, Dest holds, and there is no fault.

Postscan

Nothing.

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Example

Scenario: A delivery van logs kilometres and hours per trip. At the end of the trip the average speed is calculated for the run sheet.

Tags:

• Trip_End — Trip complete, BOOL
• Odo_km — Kilometres this trip, INT
• Hours — Hours this trip, INT
• Avg_kmh — Average speed, REAL

Rung 1:

—] [Trip_End———[DIV Odo_km  Hours  Avg_kmh]———

Scan 1 — Trip_End = 0. Odo_km reads 150 and Hours reads 4. The rung is false: Avg_kmh holds 0.

Scan 2 — Trip_End = 1. 150 ÷ 4 is written. Both sources are whole numbers, but Avg_kmh is a REAL, so the division keeps the fraction: 37.5.

Had Avg_kmh been declared INT, the same rung would show 37. Had Hours been 0, the rung would run and write nothing.

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See Also

• MUL — Multiply
• CPT — Compute (division inside a longer expression; | is the divide symbol there)
• SCP — Scale with Parameters (a ratio with an offset)
• NEQ — Not Equal (guard a divisor against zero)
• Compute Instructions — Category index

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Notes

Zero divisor. RSLogix 500 faults the processor’s math overflow bit and writes the largest value; LadderIDE skips the write and leaves Dest alone, so a display keeps showing the last good value. Put NEQ Hours 0 ahead of the DIV when a stale value would mislead.

Remainder. Total ÷ 8 into an INT gives the whole quotient. The remainder is Total − Quotient × 8, two more instructions, or a single CPT Total − TRN(Total | 8) * 8.

Large DINT values. A REAL holds about seven significant digits. Dividing a DINT in the tens of millions into a REAL Dest loses the last digits; keep a DINT Dest for exact whole-number results.

The block never colours. Watch the rung wire and the Dest value line.