Mitsubishi Electric MELSEC FX3U Programming Manual page 872

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
2) Pulse period measurement
The pulse period of the input signal from X000 is measured.
Step
0
interrupt
pointer
I001
- 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.
RUN/STOP
M8080
X000
870
X000
This duration is measured.
FNC 04
EI
M8075
M8076
Pulse width
/Pulse period
measurement
setting flag
X002
M8080
FNC 06
FEND
X000 Rising edge interrupt
M8000
FNC 12
D8078
DMOV
RUN monitor
User program
FNC 03
IRET
END
ON
pulse period
The pulse period is
not measured.
The pulse period is measured.
(D8078 and D8079 are updated.)
36 Interrupt Function and Pulse Catch Function
36.8 Pulse width/Pulse period measurement function [M8075 to M8079, D8074 to D8097]
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
D0
pulse period of input signal from X000 stored in
D8078 and D8079 is transferred to D1 and D0.
Interrupt return
RUN
one operation cycle
a
The pulse period is
not measured.
The pulse period is measured.
(D8078 and D8079 are updated.)
ON
OFF
*1
ON