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14.4
Operation
14.4.1
Duty Measurement for External Event Signal
Figure 14.2 shows an example of duty measurement for the external event signal.
1. Select the external event signal whose duty needs to be measured by the IS2 to IS0 bits in
TWCR1.
2. Select the count clock source for TWCNT by the CK2 to CK0 bits in TWCR1.
3. Write 1 to the START bit in TWCR2. At this time, TWCNT is cleared to H'00.
4. When a rising edge of the external event signal is detected, TWCNT starts counting. Then, if a
falling edge of the external event signal is detected, the TWCNT value is transferred to
TWICR. If the second rising edge of the external event signal is detected, TWCNT stops
counting. At this time, the ENDF flag in TWCR2 is set to 1.
When TWICR and TWCNT values are read and then compared, duty measurement for the
external event signal is accomplished.
External event signal
START signal
TWCNT
Duty measurement
Figure 14.2 Example of Duty Measurement for External Event Signal
Rev. 1.00, 09/03, page 406 of 704
TWCNT
clear
M
N
H'00
TWICR
X
end flag
Count stop
t
N
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