Introduction to Programming
Chapter 4
44
The condition of the Examine On instruction is either true or false:
True – the addressed memory bit is one, meaning that the corresponding
I/O device or bit is on
False – The addressed memory bit is zero, meaning that the
corresponding I/O device or bit is off
When using the Examine On instruction to address an input device, the
conventional normally open or normally closed distinctions are not made.
The Examine On instruction only checks for an on or energized status of a
device or bit (Figure 4.4).
Figure 4.4
Examine
On Instruction
||
04
()
13
112 012
Examine Off Instruction
The Examine Off instruction is the logical opposite of the Examine On
instruction. It tells the processor to check the status of the addressed
memory bit for an off condition. When addressing the I/O image table, this
instruction can examine a single input or output bit for an off voltage state
(Figure 4.5).
The condition specified by the Examine Off instruction is either true or
false:
True – The addressed memory bit is zero, meaning that the
corresponding I/O device or bit is off.
False – The addressed memory bit is one, meaning that the
corresponding I/O device or bit is on.
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