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25 HIGH-SPEED INPUT/OUTPUT FUNCTION
25.1 High-speed Counter Function
Pulse density
Pulse density is stored in the special register for each channel.
For details concerning specials registers for high-speed counters, refer to Page 719 Special Register List.
■Count direction switch during measurement
The pulse density measurement mode calculates pulse density based on difference in measuring unit time of the current
value of high-speed counters. You should therefore note that the input number of pulses may differ from the measurement
value when count direction of a high-speed counter is switched within the same measuring unit time.
When pulse density is measured, 14 pulses are input within measuring unit time, but the current value of the high-speed
counter remains "0", as shown in the following figure. As a result, pulse density is "0" for this measuring unit time.
■Operation when counting in the minus direction
Pulse density can also be measured when pulses are input in the direction whereby current value of high-speed counter is
reduced.
■Operation at overflow of high-speed counter current value
Pulse density measurement can continue even when current value of high-speed counter overflows during measurement.
■Relationship with the SPD/DSPD instruction
If pulse density measurement has already been started by the HIOEN/DHIOEN instruction, the SPD/DSPD instruction cannot
be used for the same channel.
If pulse density is currently being measured by the SPD/DSPD instruction, pulse density measurement cannot be started for
the same channel.
For details on the SPD/DSPD instruction, refer to MELSEC iQ-F FX5 Programming Manual (Instructions, Standard
Functions/Function Blocks).
■Other precautions
There are common precautions when using high-speed counters. For details, refer to Page 288 Precautions when using
high-speed counters.
Measurement
intervals
Direction
switching
Count input
Current value
10
9
8
7
6
5
4
3
2
1
0
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