Rll Equivalent; Stage Equivalent - Automation Direct DL05 User Manual

Chapter 7: RLL
PLUS
The state transition diagram to the right is a picture of
1
the solution we need to create. The beauty of it is this:
it expresses the problem independently of the
2
programming language we may use to realize it. In
other words, by drawing the diagram we have already
solved the control problem!
3
First, we'll translate the state diagram to traditional
RLL. Then we'll show how easy it is to translate the
4
diagram into a stage programming solution.

RLL Equivalent

5
The RLL solution is shown to the right. It consists of a
self-latching control relay, C0. When the On
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pushbutton (X0) is pressed, output coil C0 turns on
and the C0 contact on the second row latches itself
on. So, X0 sets the latch C0 on, and it remains on
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after the X0 contact opens. The motor output Y0 also
has power flow, so the motor is now on.
8
When the Off pushbutton (X1) is pressed, it opens the
normally-closed X1 contact, which resets the latch.
9
Motor output Y0 turns off when the latch coil C0
goes off.
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Stage Equivalent

The stage program solution is shown to the right.
The two inline stage boxes S0 and S1 correspond to
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the two states OFF and ON. The ladder rung(s)
below each stage box belong to each respective stage.
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This means that the PLC only has to scan those
rungs when the corresponding stage is active!
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For now, let's assume we begin in the OFF State, so
stage S0 is active. When the On pushbutton (X0) is
pressed, a stage transition occurs. The JMP S1
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instruction executes, which simply turns off the Stage
bit S0 and turns on Stage bit S1. So on the next PLC
A
scan, the CPU will not execute Stage S0, but will
execute stage S1!
B
In the On State (Stage S1), we want the motor to
always be on. The special relay contact SP1 is defined
as always on, so Y0 turns the motor on.
C
When the Off pushbutton (X1) is pressed, a transition back to the Off State occurs. The JMP
S0 instruction executes, which simply turns off the Stage bit S1 and turns on Stage bit S0. On
D
the next PLC scan, the CPU will not execute Stage S1, so the motor output Y0 will turn off.
The Off state (Stage 0) will be ready for the next cycle.
7–4
DL05 Micro PLC User Manual, 6th Edition, Rev. A
Stage Programming
X0
OFF
X1
Output equation Y0 = ON
Reset
Set
X0 X1
Latch
C0
SG
OFF State
S0
X0
SG
ON State
S1
Always On
SP1
X1
ON
Latch
C0
OUT
Output
Y0
OUT
Transition
S1
JMP
Output
Y0
OUT
Transition
S0
JMP