ATMEGA8_14 Datasheet, PDF (76/331 Pages) ATMEL Corporation – High-performance, Low-power Atmel

ATmega8(L)
Figure 32. 16-bit Timer/Counter Block Diagram⁽¹⁾
Count
Clear
Direction
Control Logic
clk_Tn
Timer/Counter
TCNTn
TOP BOTTOM
=
=0
=
OCRnA
=
OCRnB
ICRn
TCCRnA
Fixed
TOP
Values
ICFn (Int.Req.)
Edge
Detector
TCCRnB
TOVn
(Int. Req.)
Clock Select
Edge
Detector
Tn
( From Prescaler )
OCFnA
(Int. Req.)
Waveform
Generation
OCnA
OCFnB
(Int.Req.)
Waveform
Generation
OCnB
( From Analog
Comparator Ouput )
Noise
Canceler
ICPn
Registers
2486AA–AVR–02/2013
Note: 1. Refer to “Pin Configurations” on page 2, Table 22 on page 58, and Table 28 on page 63 for
Timer/Counter1 pin placement and description
The Timer/Counter (TCNT1), Output Compare Registers (OCR1A/B), and Input Capture Regis-
ter (ICR1) are all 16-bit registers. Special procedures must be followed when accessing the 16-
bit registers. These procedures are described in the section “Accessing 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 regis-
ters 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_T1).
The double buffered Output Compare Registers (OCR1A/B) are compared with the Timer/Coun-
ter 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 “Out-
put Compare Units” on page 83. The Compare Match event will also set the Compare Match
Flag (OCF1A/B) which can be used to generate an Output Compare interrupt request.
76