AT90USB1286-16MU ATMEL [ATMEL Corporation], AT90USB1286-16MU Datasheet - Page 125

• Manufacturer Part Number: AT90USB1286-16MU
• Description: Microcontroller with 64/128K Bytes of ISP Flash and USB Controller
• Manufacturer: ATMEL [ATMEL Corporation]

14.5
7593A–AVR–02/06
Input Capture Unit
The Timer/Counter incorporates an input capture unit that can capture external events and give
them a time-stamp indicating time of occurrence. The external signal indicating an event, or mul-
tiple events, can be applied via the ICPn pin or alternatively, for the Timer/Counter1 only, via the
Analog Comparator unit. The time-stamps can then be used to calculate frequency, duty-cycle,
and other features of the signal applied. Alternatively the time-stamps can be used for creating a
log of the events.
The Input Capture unit is illustrated by the block diagram shown in
the block diagram that are not directly a part of the input capture unit are gray shaded. The small
“n” in register and bit names indicates the Timer/Counter number.
Figure 14-3. Input Capture Unit Block Diagram
Note:
When a change of the logic level (an event) occurs on the Input Capture Pin (ICPn), alternatively
on the analog Comparator output (ACO), and this change confirms to the setting of the edge
detector, a capture will be triggered. When a capture is triggered, the 16-bit value of the counter
(TCNTn) is written to the Input Capture Register (ICRn). The Input Capture Flag (ICFn) is set at
the same system clock as the TCNTn value is copied into ICRn Register. If enabled (TICIEn =
1), the input capture flag generates an input capture interrupt. The ICFn flag is automatically
cleared when the interrupt is executed. Alternatively the ICFn flag can be cleared by software by
writing a logical one to its I/O bit location.
Reading the 16-bit value in the Input Capture Register (ICRn) is done by first reading the low
byte (ICRnL) and then the high byte (ICRnH). When the low byte is read the high byte is copied
into the high byte Temporary Register (TEMP). When the CPU reads the ICRnH I/O location it
will access the TEMP Register.
The Analog Comparator Output (ACO) can only trigger the Timer/Counter1 ICP – not
Timer/Counter3, 4 or 5.
ICPn
WRITE
ICRnH (8-bit)
TEMP (8-bit)
Comparator
Analog
ICRn (16-bit Register)
ACO*
ICRnL (8-bit)
ACIC*
DATA BUS
Canceler
ICNC
Noise
(8-bit)
TCNTnH (8-bit)
TCNTn (16-bit Counter)
AT90USB64/128
Figure
Detector
ICES
Edge
14-3. The elements of
TCNTnL (8-bit)
ICFn (Int.Req.)
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