ATMEGA325-16AJ ATMEL [ATMEL Corporation], ATMEGA325-16AJ Datasheet - Page 97

• Manufacturer Part Number: ATMEGA325-16AJ
• Description: 8-bit Microcontroller with In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Registers
2570A–AVR–09/04
Figure 40. 16-bit Timer/Counter Block Diagram
Note:
The Timer/Counter (TCNT1), Output Compare Registers (OCR1A/B), and Input Capture
Register (ICR1) are all 16-bit registers. Special procedures must be followed when
accessing the 16-bit registers. These procedures are described in the section “Access-
ing 16-bit Registers” on page 99. The Timer/Counter Control Registers (TCCR1A/B) are
8-bit registers and have no CPU access restrictions. Interrupt requests (abbreviated to
Int.Req. in the figure) signals are all visible in the Timer Interrupt Flag Register (TIFR1).
All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK1).
TIFR1 and TIMSK1 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock
source on the T1 pin. The Clock Select logic block controls which clock source and edge
the Timer/Counter uses to increment (or decrement) its value. The Timer/Counter is
inactive when no clock source is selected. The output from the Clock Select logic is
referred to as the timer clock (clk
The double buffered Output Compare Registers (OCR1A/B) are compared with the
Timer/Counter value at all time. The result of the compare can be used by the Waveform
Generator to generate a PWM or variable frequency output on the Output Compare pin
(OC1A/B). See “Output Compare Units” on page 105.. The compare match event will
1. Refer to Figure 1 on page 2, “Alternate Functions of Port D” on page 62, and “Alter-
nate Functions of Port G” on page 67for Timer/Counter1 pin placement and
description.
Timer/Counter
TCCRnA
OCRnA
OCRnB
TCNTn
ICRn
=
=
Direction
Count
Clear
T
1
).
Control Logic
ATmega325/3250/645/6450
TOP
=
TCCRnB
Values
BOTTOM
Fixed
TOP
ICFn (Int.Req.)
Detector
clk
(1)
Edge
=
Tn
0
OCnA
(Int.Req.)
OCnB
(Int.Req.)
TOVn
(Int.Req.)
Clock Select
Generation
Generation
( From Prescaler )
Waveform
Waveform
Canceler
Detector
Noise
Edge
Comparator Ouput )
( From Analog
OCnA
OCnB
ICPn
Tn
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