870
FX
3G
/FX
3U
/FX
3UC
Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
36 Interrupt Function and Pulse Catch Function
36.8 Pulse width/Pulse period measurement function [M8075 to M8079, D8074 to D8097]
2) Pulse period measurement
The pulse period of the input signal from X000 is measured.
- Timing chart
The pulse period is not measured when the input signal rises for the first time after the PLC mode is
changed from STOP to RUN, or when the input signal rises for the first time after the pulse period
measurement mode (M8080) is set to ON from OFF. (Accordingly, D8078 and D8079 are not updated.)
The pulse period is measured when the input signal rises at the next time. (As a result, D8078 and
D8079 are updated.)
Make the pulse width/pulse period measurement setting flag (M8080) remain OFF for 1 operation cycle
or more when discontinuing the pulse input.
If M8080 does not remain OFF for 1 operation cycle or more, the "a" period shown below is stored as
the pulse period.
X000
OFF
ON
This duration is measured.
FNC 04
EI
FNC 03
IRET
END
Step
0
FNC 06
FEND
I001
interrupt
pointer
X000 Rising edge interrupt
Interrupt return
Interrupts are enabled after EI (FNC 04)
instruction.
The main program is described.
X000 is used for the pulse width/pulse period
measurement function.
When X002 turns ON, the pulse period measurement
mode is actuated.
When the interrupt routine is executed at the
rising edge of the input signal from X000, the
pulse period of input signal from X000 stored in
D8078 and D8079 is transferred to D1 and D0.
*1
M8075
M8000
RUN monitor
FNC 12
DMOV
D8078
D0
User program
Pulse width
measurement
setting flag
M8076
X002
M8080
/Pulse period
M8080
RUN/STOP
RUN
X000
a
The pulse period is measured.
(D8078 and D8079 are updated.)
The pulse period is measured.
(D8078 and D8079 are updated.)
The pulse period is
not measured.
The pulse period is
not measured.
one operation cycle
ON
ON
pulse period