Page 208 - Programmable Logic Controllers, Fifth Edition - Mobile version

• With the switch open, closing PB turns on all three
pilot lights. target destination but does not contribute to logic continu-
ity. For practical purposes the label instruction is always
• When the switch is closed the jump (JMP) instruc- considered to be logically true. The operation of the pro-
tion will activate. gram can be summarized as follows:
• With the switch closed, pressing PB turns on pilot • Rungs 1, 2, 3, 8, 9, 10 are programmed outside of
lights PL1 and PL3 only. the jumped section and will always be executed as
• Rung 3 is skipped over during the PLC program normal rungs.
scan so PL2 will remain in its last state before the • If rung 4, which contains the JMP instruction, is
JMP was enabled. false, the Jump instruction is false and the jump is
Figure 9-7 illustrates the effect on input and output in- not executed.
structions of jumped rungs in a program. The label in- • Rungs 5, 6, and 7 are executed as normal and the
struction is used to identify the ladder rung that is the label instruction on rung 8 is transparent.

Inputs Ladder logic program Outputs
PB1 PB2 M
1
L1 L2
M
PB1 M PS1
TON
2 TIMER ON DELAY EN M M Timers should be
Timer T4:6 programmed outside
the jumped section.
PB2 Time base 1.0 DN
Preset 5
Accumulated 0
PL1 PL1
PS1 T4:6 PL1
3
DN
LLS1 Q2:1 SOL1
LLS1
4 JMP Jumped program rungs
are not scanned by the
LS1 SOL1 processor.
LS1
5 SOL2
Input conditions are not
examined, and outputs
LS1 LS2 SOL2
LS2 remain in their last state.
6
PL2 PL2
LS3 PL2
LS3 7
PB3 T4:6 SOL3
Q2:1 SOL3
PB3 8 LBL
DN
SOL3
LS4 SOL4
SOL3 LS4 SOL4
9
TS1 TS1 Heater Heater Heater
10

Figure 9-7 Effect on input and output instructions of jumped rungs.

Program Control Instructions Chapter 9 189

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