Pulse-Triggered Execution Of Operations - Mitsubishi Electric FX2N Beginners Manual

The Basic Instruction Set
3.4.7

Pulse-triggered execution of operations

Instruction
LDP
LDF
ANDP
ANDF
ORP
ORF
In PLC programs you will often need to detect and respond to the rising or falling edge of a bit
device's switching signal. A rising edge indicates a switch of the device value from "0" to "1", a
falling edge indicates a switch from "1" to "0".
During program execution operations that respond to rising and falling pulses only deliver a
value of "1" when the signal state of the referenced device changes.
When do you need to use this? For example, suppose you have a conveyor belt with a sensor
switch that activates to increment a counter every time a package passes it on the belt. If you
don't use a pulse-triggered function you will get incorrect results because the counter will
increment by 1 in every program cycle in which the switch registers as set. If you only register
the rising pulse of the switch signal the counter will be incremented correctly, increasing by 1
for each package.
Note Most applied instructions can also be executed by pulse signals. For details see chapter . 5).
Evaluating a rising signal pulse
Ladder Diagram
X001
0
Relay M0 is only switched on for the duration of a single
program cycle
3 – 14
Function
Load Pulse, loads on the rising edge of
the device's signal
Load Falling Pulse, loads on the falling
edge of the device's signal
AND Pulse, logical AND operation on the
rising edge of the device's signal
AND Falling Pulse, logical AND operation
on the falling edge of the device's signal
OR Pulse, logical OR operation on the
rising edge of the device's signal
OR Falling Pulse, logical OR operation
on the falling edge of the device's signal
M0
ON (1)
X1
OFF (0)
1
M0
0
An Introduction to Programming
Symbol GX Works2 FX
Instruction List
0 LDP X001
1 OUT M0
t
MITSUBISHI ELECTRIC