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FX Series Programmable Controllers Devices in Detail 4
4-23
4.11.1 Basic High Speed Counter Operation
Althou
g
h counters C235 to C255 (21 points) are all hi
g
h speed counters, the
y
share the same
ran
g
e of hi
g
h speed inputs. Therefore, if an input is alread
y
bein
g
used b
y
a hi
g
h speed
counter, it cannot be used for an
y
other hi
g
h speed counters or for an
y
other purpose, i.e as an
interrupt input.
The selection of hi
g
h speed counters are not free, the
y
are directl
y
dependent on the t
y
pe of
counter required and which inputs are available.
Available counter t
y
pes;
a) 1 phase with user start/reset: C235 to C240
b) 1 phase with assi
g
ned start/reset: C241 to C245
c) 2 phase bi-directional: C246 to C250
d) A/B phase t
y
pe: C251 to C255
Please note ALL of these counters are 32bit devices.
Hi
g
h speed counters operate b
y
the principle of interrupts. This means the
y
are event
tri
gg
ered and independent of c
y
cle time. The coil of the selected counter should be driven
continuousl
y
to indicate that this counter and its associated inputs are reserved and that other
hi
g
h speed processes must not coincide with them.
Example:
When X20 is ON, hi
g
h speed counter C235 is
selected. The counter C235 corresponds to
count input X0. X20 is NOT the counted
si
g
nal. This is the continuous drive mentioned
earlier. X0 does not have to be included in the
pro
g
ram. The input assi
g
nment is hardware
related and cannot be chan
g
ed b
y
the user.
When X20 is OFF, coil C235 is turned OFF and coil C236 is turned ON. Counter C236 has an
assi
g
ned input of X1, a
g
ain the input X20 is NOT the counted input.
The assi
g
nment of counters and input devices is dependent upon the PLC selected. This is
explained in the relevant, later sections.
Driving high speed counter coils:
• The counted inputs are NOT used to
drive the hi
g
h speed counter coils.
This is because the counter coils
need to be continuousl
y
driven ON
to reserve the associated hi
g
h speed
inputs.
Therefore, a normal non-hi
g
h speed
drive contact should be used to drive
the hi
g
h speed counter coil.
Ideall
y
the special auxiliar
y
contact M8000 should be used. However, this is not
compulsor
y
.
X20
K4789
X20
D4
C235
C236
X0
K4789
X1
D4
C235
C236