Page 96 - Programmable Logic Controllers, Fifth Edition - Mobile version

– Data Files Input module
L1
Cross reference
OFF
O0 – Output
(open)
I1 – Input

S2 – Status
ON
B3 – Binary (closed)

T4 – Timer
1 0
C5 – Counter
Word corresponding
to input module
R6 – Control
Input image
N7 – Integer

F8 – Float
Data table
files
Figure 5-3 Data file tree.
Figure 5-5 Connection of an open and closed switch to the
input image table file through the input module.
I:1 O:2
00 00
01 01
02 02 I : 1/2
03 03 Output module
04 04 01 23 L2
05 05
06 06
07 07 OFF
08 08 Input or Separator Slot Bit Bit
09 09 output numberdesignator number
10 10
11 11
12 12
13 13
14 14
15 15 O : 2/11 ON
Figure 5-4 I/O address format for the SLC family of PLCs.
Source: Image Courtesy of Rockwell Automation, Inc.
• The processor continually reads the current input
status and updates the input image table file.
The output image table file is that part of the program 0 1
memory allocated to storing the actual on/off status of con-
nected discrete outputs. Figure 5-6 shows a typical connection Word corresponding
to output module
of two pilot lights to the output image table file through the
output module. Its operation can be summarized as follows. Output image

• The status of each light (ON/OFF) is controlled by
the user program and is indicated by the presence of
1 (ON) and 0 (OFF). Data table
• Each connected output has a bit in the output image files
table file that corresponds exactly to the terminal to Figure 5-6 Connections of pilot lights to the output image
which the output is connected. table file through the output module.

Basics of PLC Programming Chapter 5 77

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