149
Limitations Each
TC number can be used as the definer in
only one TIMER or COUNTER
instruction.
Description The
CNTR(12) is a reversible, up/down circular counter
, i.e., it is used to
count
between
zero and SV according to changes in two execution conditions, those
in
the increment input (II) and those in the decrement input (DI).
The
present value (PV) will be incremented by one whenever CNTR(12) is exe
-
cuted
with an ON execution condition for II and the last execution condition for II
was OFF. The present value (PV) will be decremented by one whenever
CNTR(12)
is executed with an ON execution condition for DI and the last execu
-
tion
condition for DI was OFF
. If OFF to ON changes have occurred in both II and
DI since the last execution, the PV will not be changed.
If
the execution conditions have not changed or have changed from ON to OFF
for both II and DI, the PV of CNT will not be changed.
When
decremented from 0000, the present value is set to SV and the Comple
-
tion Flag is turned ON until the PV is decremented again. When incremented
past
the SV
, the PV is set to 0000 and the Completion Flag is turned ON until the
PV is incremented again.
CNTR(12)
is reset with a reset input, R. When R goes from OFF to ON, the PV is
reset to zero. The PV will not be incremented or decremented while R is ON.
Counting will begin again when R goes OFF
. The PV for CNTR(12) will not be
reset in interlocked program sections or by the effects of power interruptions.
Changes
in II and DI execution conditions, the Completion Flag, and the PV are
illustrated below starting
from
part way through CNTR(12) operation (i.e., when
reset,
counting begins from zero). PV line height is meant to indicate changes in
the
PV only
.
Execution
condition
on increment (II)
Execution condition
on decrement (DI)
ON
OFF
ON
OFF
Completion Flag
ON
OFF
PV
SV
SV
– 1
SV – 2
0001
0000
0000
SV
SV – 1
SV – 2
Precautions Program
execution will continue even if a non-BCD SV is used, but the SV will
not be correct.
Flags ER:
SV is not in BCD.
Indirectly
addressed DM word
is non-existent. (Content of
∗
DM word is
not BCD, or the DM area boundary has been exceeded.)
Timer and Counter Instructions Section 5-14
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