236
Timer and Counter Instructions
Section 5-16
Changes in execution conditions, the Completion Flag, and the PV are illus-
trated below. PV line height is meant only to indicate changes in the PV.
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 EM/DM word is non-existent.
(Content of
*
EM/
*
DM word is not BCD, or the EM/DM area boundary
has been exceeded.)
Example
In the following example, CNT is used to create extended timers by counting
SR area clock pulse bits.
CNT 001 counts the number of times the 1-second clock pulse bit (SR 25502)
goes from OFF to ON. Here again, IR 00000 is used to control the times when
CNT is operating.
Because in this example the SV for CNT 001 is 700, the Completion Flag for
CNT 002 turns ON when 1 second x 700 times, or 11 minutes and 40 seconds
have expired. This would result in IR 01602 being turned ON.
!Caution
The shorter clock pulses will not necessarily produce accurate timers
because their short ON times might not be read accurately during longer
cycles. In particular, the 0.02-second and 0.1-second clock pulses should not
be used to create timers with CNT instructions.
Execution condition
on count pulse (CP)
Execution condition
on reset (R)
ON
OFF
ON
OFF
Completion Flag
ON
OFF
PV
SV
SV
−
1
SV
−
2
0002
0001
0000
SV
CP
R
CNT
001
#0700
00000 25502
00001
CNT 001
01602
Address
Instruction
Operands
00000
LD
00000
00001
AND
25502
00002
LD NOT
00001
00003
CNT
001
#
0700
00004
LD
CNT
001
00005
OUT
01602
