Rockwell Automation 9323-PA1E QUICK START GUIDE APS 6.0 - Manual (Page 22)

Control Basics
2–5
How External I/O Devices Communicate with the
Processor
The figures that follow apply to a modular controller demo unit having an input
module in slot 1 and an output module in slot 3. See page 1–3 for a diagram of the
slot location. To simplify the illustration, only pushbutton 0 and pilot light 0 of the
external I/O are shown.
Each of the external input circuits is represented by a status bit in the input data file
of the processor file. Each of the external output circuits is represented by a status
bit in the output data file of the processor file. During controller operation, the
processor applies the input data to the program, solves the program based on the
instruction you enter, and energizes and de-energizes external outputs.
SLC 5/01 CPU INPUT
INPUT
IN 0
INPUT
IN 1
IN 2
IN 3
F8
0
Input Data File
address data
I:1 0000
Input Module in slot 1
Status bit 0 corresponds
to terminal 0 of the input
module in slot 1.
Pushbutton 0 is wired to terminal 0.
Pressing pushbutton 0 will cause the
corresponding status bit in the input
data file to go from 0 to 1.
Closing an external input circuit changes the corresponding status bit from 0 to 1.
Opening an external input circuit changes the corresponding status bit from 1 to 0.