Mitsubishi Electronics FX1S Driving high speed counter coils, Basic High Speed Counter Operation

FX Series Programmable Controllers Devices in Detail 4

4.11.1Basic High Speed Counter Operation

Although counters C235 to C255 (21 points) are all high speed counters, they share the same range of high speed inputs. Therefore, if an input is already being used by a high speed counter, it cannot be used for any other high speed counters or for any other purpose, i.e as an interrupt input.

The selection of high speed counters are not free, they are directly dependent on the type of counter required and which inputs are available.

Available counter types;

a)1 phase with user start/reset: C235 to C240

b)1 phase with assigned start/reset: C241 to C245

c)2 phase bi-directional: C246 to C250

d)A/B phase type: C251 to C255

Please note ALL of these counters are 32bit devices.

High speed counters operate by the principle of interrupts. This means they are event triggered and independent of cycle time. The coil of the selected counter should be driven continuously to indicate that this counter and its associated inputs are reserved and that other high speed processes must not coincide with them.

Example:

When X20 is ON, high speed counter C235 is selected. The counter C235 corresponds to count input X0. X20 is NOT the counted signal. This is the continuous drive mentioned earlier. X0 does not have to be included in the program. The input assignment is hardware related and cannot be changed by the user.

X20	C235
X20	K4789
	C236
	D4

When X20 is OFF, coil C235 is turned OFF and coil C236 is turned ON. Counter C236 has an assigned input of X1, again the input X20 is NOT the counted input.

The assignment 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 high speed counter coils.	X0
This is because the counter coils		C235
need to be continuously driven ON	X1	K4789
to reserve the associated high speed
		C236
inputs.
		D4
Therefore, a normal non-high speed

drive contact should be used to drive the high speed counter coil.

Ideally the special auxiliary contact M8000 should be used. However, this is not compulsory.

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