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Chapter 4. Ladder Diagram (LD) Programming
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When ONDTR is used in a program block that is not called every scan, it accumulates time
between calls to the program block unless it is reset. This means that ONDTR functions like a
timer operating in a program with a much slower scan than the timer in the main program block.
For program blocks that are inactive for a long time, ONDTR should be programmed to allow for
this catch-up feature. For example, if a timer in a program block is reset and the program block is
not called (is inactive) for four minutes, when the program block is called, four minutes of time
will already have accumulated. If the enable input is ON and the reset input is OFF, these four
minutes are applied to the timer (that is, CV is set to 4 minutes).
Timing diagram
ENABLE
RESET
Q
A
B
A. ENABLE goes high; timer starts accumulating.
B. Current value (CV) reaches preset value (PV); Q goes high. Timer continues to accumulate time
until ENABLE goes low, RESET goes high or current value becomes equal to the maximum time.
C. RESET goes high; Q goes low, accumulated time is reset (CV=0).
D. RESET goes low; timer then starts accumulating again, as ENABLE is high.
E. ENABLE goes low; timer stops accumulating. Accumulated time stays the same.
F. ENABLE goes high again; timer continues accumulating time.
G. CV becomes equal to PV; Q goes high. Timer continues to accumulate time until ENABLE goes
low, RESET goes high or CV becomes equal to the maximum time.
H. ENABLE goes low; timer stops accumulating time.
Operands for On Delay Stopwatch Timer
Parameter Description
Address
Beginning address of a three-word WORD array:
(????)
Word 1: Current value (CV)
Word 2: Preset value (PV)
Word 3: Control word
R
When R is ON, it resets the Current Value (Word 1) to zero.
PV
The Preset Value, used when the timer is enabled or reset.
0 PV +32,767. If PV is out of range, it has no effect on Word 2.
CV
Current Value of the timer
224
PACSystems* RX7i, RX3i and RSTi-EP CPU Programmer's Reference Manual
C
D
E
F G
Do not use the Address, Address+1, or Address+2
addresses with other instructions. Overlapping
references cause erratic timer operation.
H
Warning
Allowed Operands Optional
R, W, P, L, symbolic
No
Power flow
Optional
All except S, SA, SB,
Optional
SC
All except S, SA, SB,
Optional
SC and constant
GFK-2950C
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