I:1 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 Data Files Figure 5-3 Data file tree. 0 1 2 3 Cross reference O0 – Output I1 – Input S2 – Status B3 – Binary T4 – Timer C5 – Counter R6 – Control N7 – Integer F8 – Float I : 1/2 Input or Separator output Slot number Bit number Bit designator – O:2 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 O : 2/11 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 memory allocated to storing the actual on/off status of connected discrete outputs. Figure 5-6 shows a typical connection of two pilot lights to the output image table file through the output module. Its operation can be summarized as follows. • 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). • Each connected output has a bit in the output image table file that corresponds exactly to the terminal to which the output is connected. 1 0 Word corresponding to input module Input image Input module OFF (open) ON (closed) L1 Data table files Figure 5-5 Connection of an open and closed switch to the input image table file through the input module. Output module 0 1 Word corresponding to output module Output image OFF L2 Data table files ON Figure 5-6 Connections of pilot lights to the output image table file through the output module. Basics of PLC Programming Chapter 5 77
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