RLL
P
LUS
Stage
Programming
7--16
RLL
PLUS
Stage Programming
DL105 PLC User Manual, 3rd Edition
We can think of states or stages as simply dividing up our ladder program as
depicted in the figure below. Each stage contains only the ladder rungs which are
needed for the corresponding state of the process. The logic for transitioning out of a
stage is contained within that stage. It’s easy to choose which ladder rungs are active
at powerup by using an “initial” stage type (ISG).
Stage 0
Stage 1
Stage 2
Most all instructions work just like they do in standard RLL. You can think of a stage
just like a miniature RLL program which is either active or inactive.
Output Coils
-- As expected, output coils in active stages will turn on or off outputs
according to power flow into the coil. However, note the following:
S
Outputs work as usual, provided each output reference (such as “Y3”) is
used in only one stage.
S
An output can be referenced from more than one stage, as long as only
one of the stages is active at a time.
S
If an output coil is controlled by more than one stage simultaneously, the
active stage nearest the bottom of the program determines the final
output status during each scan. Therefore, use the OROUT instruction
instead when you want multiple stages to have a logical OR control of
an output.
One-Shot or PD coils
-- Use care if you must use a Positive Differential coil in a
stage. Remember that the input to the coil must make a 0--1 transition. If the coil is
already energized on the first scan when the stage becomes active, the PD coil will
not work. This is because the 0--1 transition did not occur.
PD coil alternative: If there is a task which you want to do only once (on 1 scan), it can
be placed in a stage which transitions to the next stage on the same scan.
Counter
-- In using a counter inside a stage, the stage must be active for one scan
before the input to the counter makes a 0--1 transition. Otherwise, there is no real
transition and the counter will not count.
The ordinary Counter instruction does have a restriction inside stages: it may not be
reset from other stages using the RST instruction for the counter bit. However, the
special Stage Counter provides a solution (see next paragraph).
Stage Counter
-- The Stage Counter has the benefit that its count may be globally
reset from other stages by using the RST instruction. It has a count input, but no reset
input. This is the only difference from a standard counter.
Drum
-- Realize that the drum sequencer is its own process, and is a different
programming method than stage programming. If you need to use a drum with
stages, be sure to place the drum instruction in an ISG stage that is always active.
How Instructions
Work Inside Stages
Summary of Contents for DL105
Page 2: ...DL105 PLC User Manual Manual Number D1 USER M...
Page 308: ...1B DL105 Error Codes In This Appendix Error Code Table...
Page 314: ...1C Instruction Execution Times In This Appendix Introduction Instruction Execution Times...
Page 324: ...1D Special Relays In This Appendix DL105 PLC Special Relays...
Page 327: ...1E PLC Memory In This Appendix DL105 PLC Memory...
