Math Instructions

Perform arithmetic on two numeric sources and write the result to a destination tag. Math instructions act like coils — place them on the right side of a rung.

Available Math Instructions

Instruction	Symbol	Purpose
ADD	ADD Source A sourceA Source B sourceB Dest dest	Writes sourceA + sourceB into the destination tag.
SUB	SUB Source A sourceA Source B sourceB Dest dest	Writes sourceA − sourceB into the destination tag.
MUL	MUL Source A sourceA Source B sourceB Dest dest	Writes sourceA × sourceB into the destination tag.
DIV	DIV Source A sourceA Source B sourceB Dest dest	Writes sourceA ÷ sourceB into the destination tag. DINT ÷ DINT truncates toward zero; guard against divide-by-zero.

Operands

Name	Type
sourceA	DINT | REAL
sourceB	DINT | REAL
dest	DINT | REAL

How It Works

When the rung is true, the instruction reads both sources, performs the operation, and writes the result to the destination — once per scan. If the rung stays true, the instruction runs every scan.

Example — Running Total

XIC(PartDetected)ONS(EdgeBit)ADD(TotalParts,1,TotalParts)

Each rising edge of PartDetected adds 1 to TotalParts.

Example — Scale a Reading

Convert a raw ADC value (0–4095) into a percentage (0–100).

MUL(RawValue,100,Scaled);DIV(Scaled,4095,Scaled)

If Scaled is a DINT, the final division truncates — RawValue = 2047 becomes Scaled = 50, not 49.97. Declare Scaled as REAL if you need the fractional precision.

Data Type Notes

• DINT / DINT truncates (integer division). 10 / 3 = 3.
• Mixing DINT and REAL: the result is promoted to REAL. Make sure the destination matches.
• DIV by zero produces a fault. Guard with a compare:

NE(Divisor,0)DIV(Numerator,Divisor,Result)

Common Mistakes

• Running an ADD accumulator without an ONS — the value runs away as it adds every scan.
• Expecting integer division to round — it truncates toward zero.
• Writing the operation the wrong way around — the destination is the last operand.

Related

• MOVE — copy a value without computing
• Compare instructions — act on the result of a calculation
• One Shot — guard per-scan accumulation