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FX Series Programmable Controllers Devices in Detail 44.11.1 Basic High Speed Counter OperationAlthough counters C235 to C255 (21 points) are all high speed counters, they share the samerange of high speed inputs. Therefore, if an input is already being used by a high speedcounter, it cannot be used for any other high speed counters or for any other purpose, i.e as aninterrupt input.The selection of high speed counters are not free, they are directly dependent on the type ofcounter required and which inputs are available.Available counter types;a) 1 phase with user start/reset: C235 to C240b) 1 phase with assigned start/reset: C241 to C245c) 2 phase bi-directional: C246 to C250d) A/B phase type: C251 to C255Please note ALL of these counters are 32bit devices.High speed counters operate by the principle of interrupts. This means they are eventtriggered and independent of cycle time. The coil of the selected counter should be drivencontinuously to indicate that this counter and its associated inputs are reserved and that otherhigh speed processes must not coincide with them.Example:When X20 is ON, high speed counter C235 isselected. The counter C235 corresponds to X20C235count input X0. X20 is NOT the countedsignal. This is the continuous drive mentioned X20K4789earlier. X0 does not have to be included in theC236program. The input assignment is hardwareD4related and cannot be changed by the user.When X20 is OFF, coil C235 is turned OFF and coil C236 is turned ON. Counter C236 has anassigned 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 isexplained in the relevant, later sections.Driving high speed counter coils:• The counted inputs are NOT used todrive the high speed counter coils.X0This is because the counter coilsC235need to be continuously driven ONX1K4789to reserve the associated high speedC236inputs.D4Therefore, a normal non-high speeddrive contact should be used to drivethe high speed counter coil.Ideally the special auxiliary contact M8000 should be used. However, this is notcompulsory.4-23