Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 97)

Math Instructions
Chapter 10
10Ć9
bit 14 - overflow/underflow/illegal bit; significance depends on the
arithmetic operation being performed at the time
overflow (addition) - set indicates result exceeds displayable result
overflow (subtraction) - set indicates result exceeds displayable result
overflow or underflow (multiplication) - set indicates result exceeds
displayable result
illegal (division) - set indicates division by zero or result exceeds result
word range
In this section, unused status bits are shown blank for the following reasons:
Whether the content of an unused status bit in an input word is 0 or 1 is
irrelevant as such bits are ignored in EAF instruction execution.
The EAF instruction reset unused status bits in result words. For simplicity
the bits are left blank.
The processor can “chain” the results of the last executed EAF instruction with
the current EAF instruction. You can use the last result as either the augend,
minuend, multiplicand or dividend. Or, you can also use the last result as either
the addend, subtrahend, multiplier or divisor.
Branch Instructions
The least amount of instructions required to make the processor execute an EAF
instruction is shown in Figure 10.1. The instructions composing the three terms
A, B, and C are probably in different locations of your ladder diagram. Chances
are that you would never see them. You can monitor the values in these
instructions using the ladder diagram shown in Figure 10.4. The ladder diagram
serves two purposes. It contains both the least amount of instructions required
to execute an EAF instruction and display branches. Therefore, you have a
choice of using either one of two ladder diagrams to execute an EAF
instruction. These two ladder diagrams are named:
primary
optional