Mitsubishi Digital Electronics FX2C Manual

A SERVICE OF

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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