Data Table
Chapter 3
321
The hardware-program interface is illustrated in Figure 3.7 by showing
the operational relationship between the input and output devices, the
input/output image table and the user program.
When an input device connected to terminal 113/12 is closed, the input
module circuitry senses a voltage. The On condition is reflected in the
input image table bit 113/12. During the program scan, the processor
examines bit 113/12 for an On (1) condition. If the bit is On (1), the
Examine On instruction is logically true. A true condition is displayed as
an intensified instruction. A path of logic continuity is established and
causes the rung to be true. The processor then sets output image table bit
012/06 to On (1). The processor turns on terminal 012/06 during the next
I/O scan and the output device wired to this terminal becomes energized.
When the rung condition is true, the output instruction is intensified.
3.3.3
Fundamental Operation
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