Preface
MicroLogix 1000 Programmable Controllers User Manual
8–2
About the Math Instructions
These instructions perform the familiar four function math operations. The majority
of the instructions take two input values, perform the specified arithmetic function,
and output the result to an assigned memory location.
For example, both the ADD and SUB instructions take a pair of input values, add or
subtract them, and place the result in the specified destination. If the result of the
operation exceeds the allowable value, an overflow or underflow bit is set.
To learn more about the math instructions, we suggest that you read the Math
Instructions Overview that follows.
Math Instructions Overview
The following general information applies to math instructions.
Using Indexed Word Addresses
You have the option of using indexed word addresses for instruction parameters
specifying word addresses. Indexed addressing is discussed in chapter 5.
Updates to Arithmetic Status Bits
The arithmetic status bits are found in Word 0, bits 0–3 in the controller status file.
After an instruction is executed, the arithmetic status bits in the status file are
updated:
With this Bit:
The Controller:
S:0/0
Carry (C)
sets if carry is generated; otherwise cleared.
S:0/1
Overflow (V)
indicates that the actual result of a math instruction does not fit
in the designated destination.
S:0/2
Zero (Z)
indicates a 0 value after a math, move, or logic instruction.
S:0/3
Sign (S)
indicates a negative (less than 0) value after a math, move, or
logic instruction.
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