ATMEGA8L ATMEL [ATMEL Corporation], ATMEGA8L Datasheet - Page 75

• Manufacturer Part Number: ATMEGA8L
• Description: 8-bit AVR with 8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Registers
2486M–AVR–12/03
Figure 32. 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 77. 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 (TIFR).
All interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK).
TIFR and TIMSK are not shown in the figure since these registers are shared by other
timer units.
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 83. The Compare Match event will also
1. Refer to “Pin Configurations” on page 2, Table 22 on page 56, and Table 28 on page
61 for Timer/Counter1 pin placement and description.
Timer/Counter
TCCRnA
OCRnA
OCRnB
TCNTn
ICRn
=
=
Direction
Count
Clear
T
1
).
Control Logic
TOP
=
TCCRnB
Values
BOTTOM
Fixed
TOP
ICFn (Int.Req.)
(1)
Detector
clk
Edge
=
Tn
0
OCFnA
(Int. Req.)
OCFnB
(Int.Req.)
TOVn
(Int. Req.)
Clock Select
Generation
Generation
( From Prescaler )
Waveform
Waveform
Canceler
ATmega8(L)
Detector
Noise
Edge
Comparator Ouput )
( From Analog
OCnB
OCnA
ICPn
Tn
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