Mitsubishi FX1N Series Programming Manual

FX Series Programmable Controllers Points Of Technique 10
10-4
10.4 Constant Scan Mode
Some times the timing of operations can be a problem, especially if some co-ordination is
being attempted with a second control system. In cases like this it is very useful to fix the
PLC’s scan time. Under normal conditions the PLC’sscantimewillvaryfromonescantothe
next. This is simply because the natural PLC scan time is dependent on the number of and
type of the active instructions. As these are continually changing between program scans the
actual scan time is also a varying. Hence, by using the additional program function identified
below, the PLC’s scan time can be fixed so that it will be the same duration on every program
scan. The actual scan duration is set by writing a scan time in excess of the current longest
scan duration to special data register D8039 (in the example the value K150 is used). If the
PLC scans the program quicker than the set scan time, a 'pause' will occur until the set scan
duration is reached.
This program example should be placed at the beginning of a users program.
10.5 Alternating ON/OFF States
It is often useful to have a single input control or toggle a situation. A basic, yet typical example
is the switching ON/OFF of a Light. This can be easily achieved by using standard ladder
program to load an input and switch an output. However, this system requires an input which is
latchable. If basic ladder steps are used to latch the program then it soon becomes complex
and prone to mis-programming by the user. Using the ALT instruction to toggle the ON/OFF
(SET/RESET, START/STOP, SLOW/FAST) state is much simpler, quicker and more efficient.
Explanation:
Pressing the momentary push button X1 once will switch the lamp ON. Pressing the push
button for a second time will cause the lamp to turn OFF. And if the push button is again
pressed for a third time, the lamp is turned ON again and so the toggled status continues.
The second program shown identifies a possible motor interlock/control, possibly a start/stop
situation.
FX 1S
FX 1N FX 2N
FX 2NC
M8000
M8039
MOV
K150
D8039
Newly set
constant scan
time = 150 msec
FX 1S
FX 1N FX 2N
FX 2NC
X 0
ALT Y 1
X 0 Y 1
X 0
Y 0
Y 1
M 0
M 0
ALT M 0
Program
example 1
Program example 2

Mitsubishi FX1N Series Specifications

General

Brand	Mitsubishi
Model	FX1N Series
Category	Controller
Language	English