Omron SYSMAC C20K Operation Manual page 101

Timer and Counter Instructions
5-11-4 COUNTER – CNT
Limitations
Description
Precautions
Flags
90
Ladder Symbol
CP
R
Each TC number can be used as the definer in only one timer or counter in-
struction.
CNT is used to count down from SV when the execution condition on the
count pulse, CP, goes from OFF to ON, i.e., the present value (PV) will be
decremented by one whenever CNT is executed with an ON execution condi-
tion for CP and the execution condition was OFF for the last execution. If the
execution condition has not changed or has changed from ON to OFF, the
PV of CNT will not be changed. Counter is turned ON when the PV reaches
zero and will remain ON until the counter is reset.
CNT is reset with a reset input, R. When R goes from OFF to ON, the PV is
reset to SV. The PV will not be decremented while R is ON. Counting down
from SV will begin again when R goes OFF. The PV for CNT will not be reset
in interlocked program sections or for power interruptions.
Changes in execution conditions, the completion flag, and the PV are illus-
trated below. PV line height is meant to indicate changes in the PV only.
Execution condition
ON
on count pulse (CP)
OFF
Execution condition
ON
on reset (R)
OFF
ON
Completion flag
OFF
PV
Program execution will continue even if a non-BCD SV is used, but the SV
will not be correct.
ER: SV is not in BCD.
CNT N
Operand Data Areas
SV
SV: Set value (word, BCD)
SV
SV - 1
SV - 2
Section 5-11
Definer Values
N: TC number
# (00 through 47)
IR, HR, #
SV
0002
0001
0000