What Stage Bits Do; Stage Instruction Characteristics - Automation Direct DL05 User Manual

Chapter 7: RLL
PLUS
We can mark our desired powerup state as shown to
1
the right, which helps us remember to use the
appropriate Initial Stages when creating a stage
2
program. It is permissible to have as many initial stages
as the process requires.
3

What Stage Bits Do

You may recall that a stage is just a section of ladder program which is either active or inactive
at a given moment. All stage bits (S0 to S377) reside in the PLC's image register as individual
4
status bits. Each stage bit is either a boolean 0 or 1 at any time.
Program execution always reads ladder rungs from top to bottom, and from left to right. The
5
drawing below shows the effect of stage bit status. The ladder rungs below the stage
instruction continuing until the next stage instruction or the end of program belong to stage
6
0. Its equivalent operation is shown on the right. When S0 is true, the two rungs have power
flow.
7
• If Stage bit S0 = 0, its ladder rungs are not scanned (executed).
• If Stage bit S0 = 1, its ladder rungs are scanned (executed).
8
9
10
11

Stage Instruction Characteristics

12
The inline stage boxes on the left power rail divide the ladder
program rungs into stages. Some stage rules are:
13
• Execution – Only logic in active stages are executed on any
scan.
14
• Transitions – Stage transition instructions take effect on the
next occurrence of the stages involved.
A
• Octal numbering – Stages are numbered in octal, like I/O
points, etc. So "S8" is not valid.
• Total Stages – The DL05 offers up to 256 stages (S0 to S377 in
B
octal).
• No duplicates – Each stage number is unique and can be used
C
just once.
• Any order – You can skip numbers and sequence the stage
D
numbers in any order.
• Last Stage – the last stage in the ladder program includes all
rungs from its stage box until the end coil.
7–6
DL05 Micro PLC User Manual, 6th Edition, Rev. A
Stage Programming
Actual Program Appearance
SG
S0
Powerup
OFF
Functionally Equivalent Ladder
S0
(includes all rungs in stage)
SG
S0
SG
S1
SG
S2
X0
ON
X1
END