Mitsubishi MELSEC-A series, Programming Manual

Page: 191 / 508

6. BASIC INSTRUCTIONS
6
−
79
MELSEC-A
Timing of Timer Used with CHG Instruction
Each of the CPUs with which the CHG instruction can be used has two timer set
value storage areas; one for the main sequence program and the other for the
subsequence program.
In these areas, the set value of the timer not in use is 0. The set value of 0 is
regarded as infinite and the timer does not time out.
When the main (sub) sequence program is switched to the sub (main) sequence
program by the CHG instruction after the timer in the main (sub) sequence program
has started timing, the timer does not time out during execution of the sub (main)
program because the timer set value specified in the main (sub) program is 0 in the
sub (main) program timer set value storage area.
Ladder example
The following program is written after the main sequence program and the same timer number is not used in
the subsequence program.
Timing chart
Operation
T200 started by the main sequence program does not time out while the subsequence program is running.
It times out on the following condition when the main sequence program is run again:
(Present value) < 0 or (set value) < (present value)
(
)
X000
K15
T200
Main sequence
program run
Subsequence
program run
X0
T200 coil
The timer does not time out as
the set value in the sub-
sequence program is 0.
The timer times out as the
set value is greater than the
present value. In this case,
the value monitored is 15.
T200 contact
T200 coil is not switched off as
OUT T200 is not executed when
X0 is switched off.
10ms timer tim-
ing value
T200 present
value