Copyright Goodheart-Willcox Co., Inc. 104 Programmable Logic Controllers: Hardware and Programming you to see the operation of a running PLC control system on the computer screen. You can use this mode to troubleshoot the PLC program while it is actually controlling the input/output devices. Figure 6-27 displays the input/output connections of an Allen-Bradley fixed SLC 500 PLC device for the relay logic diagram shown in Figure 6-26. Table 6-5 illustrates the I/O port assignments. Stop Start CR L1 L2 CR-1 CR-2 Jog Motor Bell Goodheart-Willcox Publisher Figure 6-26. Relay logic diagram. 0000 0001 0002 0003 0004 0005 Switch #1 Latch #1 B3:0 I:0 0 0 L End Switch #2 Latch #2 B3:0 I:0 1 1 L Pushbutton #1 Latch #1 B3:0 I:0 2 0 U Pushbutton #2 Latch #2 B3:0 I:0 3 1 U Latch #1 Green light O:0 B3:0 0 0 Latch #2 Red light O:0 B3:0 1 1 0006 Goodheart-Willcox Publisher Figure 6-25. PLC ladder logic diagram for the relay logic diagram shown in Figure 6-22.