Rockwell Automation 1772-L8_LW_LWP_LX_LXP,D17726.5.8 User Manual - Manual (Page 120)

Scan Theory
Chapter 8
8-2
Figure 8.1
The Processor Scans With This Sequence
10351-I
Output
Image
Table
Input
Terminals
Input
Image
Table
Output
Terminals
Copy output image table status
into output terminal circuits.
Copy input terminal status into
input image table
Program Statement
Execute each program rung in
sequence, writing into bits in the
data table, including the output
image table.
( )
I/O
Scan
Program
Scan
Upon power-up, the processor begins the scan sequence with a program
pre-scan. The processor then proceeds with the I/O scan. Data from output
image table is written to the output modules. Data from the input modules
is read into the input image table.