ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 98

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

14.6
98
Input Capture Unit
Atmel ATtiny24/44/84 [Preliminary]
The Timer/Counter Overflow Flag (TOV1) is set according to the mode of operation selected
by the WGM13:0 bits. TOV1 can be used for generating a CPU interrupt.
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
multiple events, can be applied via the ICP1 pin or, alternatively, 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 elements of the block diagram that are not directly a part of the input capture unit are
shaded gray. The small "n" in register and bit names indicates the timer/counter number.
Figure 14-3. Input Capture Unit Block Diagram
When a change of the logic level (an event) occurs on the input capture pin (ICP1), or alterna-
tively on the analog comparator output (ACO), and this change conforms to the setting of the
edge detector, a capture will be triggered. When a capture is triggered, the 16-bit value of the
counter (TCNT1) is written to the input capture register (ICR1). The input capture flag (ICF1) is
set at the same system clock as the TCNT1 value is copied into ICR1 register. If enabled
(ICIE1 = 1), the input capture flag generates an input capture interrupt. The ICF1 flag is auto-
matically cleared when the interrupt is executed. Alternatively, the ICF1 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 (ICR1) is done by first reading the low
byte (ICR1L) and then the high byte (ICR1H). When the low byte is read, the high byte is cop-
ied into the high byte temporary register (TEMP). When the CPU reads the ICR1H I/O
location, it will access the TEMP register.
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)
Detector
ICES
Edge
Figure 14-3 on page
TCNTnL (8-bit)
ICFn (Int.Req.)
7701E–AVR–02/11
98.