RLL
P
LUS
Stage
Programming
7--5
RLL
PLUS
Stage Programming
DL105 PLC User Manual, 3rd Edition
Right now, you may be thinking “I don’t see the big advantage to Stage
Programming... in fact, the stage program is longer than the plain RLL program”.
Well, now is the time to exercise a bit of faith. As control problems grow in complexity,
stage programming quickly out-performs RLL in simplicity, program size, etc.
For example, consider the diagram below.
Notice how easy it is to correlate the OFF
and ON states of the state transition diagram
below to the stage program at the right. Now,
we challenge anyone to easily identify the
same states in the RLL program on the
previous page!
S1
X0
JMP
SG
S0
S0
X1
JMP
SG
S1
OUT
Y0
OFF State
ON State
SP1
OFF
ON
X0
X1
At powerup and Program-to-Run Mode
transitions, the PLC always begins with all
normal stages (SG) off. So, the stage
programs shown so far have actually had no
way to get started (because rungs are not
scanned unless their stage is active).
Assume that we want to always begin in the
Off state (motor off), which is how the RLL
program works. The Initial Stage (ISG) is
defined to be active at powerup. In the
modified program to the right, we have
changed stage S0 to the ISG type. This
ensures the PLC will scan contact X0 after
powerup, because Stage S0 is active.
After
powerup, an Initial Stage (ISG) works just
like any other stage!
We can change both programs so that the
motor is ON at powerup. In the RLL below, we
must add a first scan relay SP0, latching C0
on. In the stage example to the right, we
simply make Stage S1 an initial stage (ISG)
instead of S0.
S1
X0
JMP
ISG
S0
S0
X1
JMP
SG
S1
OUT
Y0
Initial Stage
SP1
S1
X0
JMP
SG
S0
S0
X1
JMP
ISG
S1
OUT
Y0
Initial Stage
SP1
X1
X0
OUT
C0
OUT
Y0
C0
First Scan
SP0
Powerup in OFF State
Powerup in ON State
Powerup in ON State
NOTE:
If the ISG is within the retentive range for stages, the ISG will remain in the
state it was in before power down and will NOT turn itself on during the first scan.
Let’s Compare
Initial Stages
Содержание DL105
Страница 2: ...DL105 PLC User Manual Manual Number D1 USER M...
Страница 308: ...1B DL105 Error Codes In This Appendix Error Code Table...
Страница 314: ...1C Instruction Execution Times In This Appendix Introduction Instruction Execution Times...
Страница 324: ...1D Special Relays In This Appendix DL105 PLC Special Relays...
Страница 327: ...1E PLC Memory In This Appendix DL105 PLC Memory...
Страница 329: ...1F European Union Directives CE In This Appendix European Union EU Directives Basic EMC Installation Guidelines...