Page 282 - Programmable Logic Controllers, Fifth Edition - Mobile version

Output
L1 Inputs Ladder logic program Module O:2 L2
S1 SQO
SEQUENCER OUTPUT 0
File #B3:0 EN 1
Mask F0FF 2
S1 DN
S2 Dest O:2 3
Control R6:0 4
Length 8 5
Position 2
S2 6
7
8
9
10
S1 S2 11
12
13
Field triggered input events
14
15
15 11 10 98 0 Destination
0000 0000 11 11 O:2 Current step Pos 2

1111 0000 1111 11 11 Mask

Pos File
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 #B3:0
1 0 0 1 1 0 0 0 0 0 0 1 1 0 0 1 1
Pos 2 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1
3 1 1 0 0 0 0 0 0 1 1 0 0 1 1 0 0
4 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1
5 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0
6 0 0 1 1 0 0 0 0 1 1 1 1 1 1 1 1
7 0 0 0 1 0 0 0 0 0 0 0 1 1 1 1 1
8 0 1 0 1 0 0 0 0 0 1 0 1 0 1 0 1
Figure 12-18 Event-driven sequencer output program.

are identical to the data stored in the sequencer file, the • The mask (F000h) allows unused bits of the
control found bit is set to 1. sequencer instruction to be used independently.
An example of an SLC 500 sequencer compare (SQC) In this example, unused bit I:1/0 is used for the
instruction program is shown in Figure 12-19. The opera- conditional input of the sequencer compare
tion of the program can be summarized as follows: rung.
• The data in the highest 4 bits of the source (I:1) The sequencer load (SQL) instruction is used to read
are compared to the data in file #B3:22. the PLC input module and store the input data in the
• In this example, the highest 4 bits in I:1 match sequencer file. Loading input conditions for a large num-
the status of the highest 4 bits in B3:25 at step ber of process steps is prone to errors. In such instances
position 3. the sequencer load instruction can be used to load data
• If the pushbutton input I:1/0 is true at this point, into a sequencer file one step at a time. For example, a
the found (FD) bit is set, which turns output robot may be jogged manually through its sequence of
PL1 on. operation, with its input devices read at each step. At
• Whenever the combination of opened and closed each step, the status of the input devices is written to
switches connected to I:1/12, I:1/13, I:1/14, and the data file in the sequencer compare instruction. As a
I:1/15 is equal to the combination of 1s and 0s result, the file is loaded with the desired input status at
on a step in the sequencer reference file and the each step, and these data are then used for comparison
input I:1/0 is true, the PL1 output will become with the input devices when the machine is run in auto-
energized. matic mode.

Sequencer and Shift Register Instructions Chapter 12 263

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