ATmega128(L)
Figure 46. 16-bit Timer/Counter Block Diagram
Count
TOVx
(Int.Req.)
Clear
Control Logic
Direction
Clock Select
TCLK
Edge
Detector
Tx
TOP BOTTOM
( From Prescaler )
Timer/Counter
TCNTx
=
= 0
OCFxA
(Int.Req.)
Waveform
Generation
OCxA
OCxB
OCxC
=
OCRxA
OCFxB
(Int.Req.)
Fixed
TOP
Values
Waveform
Generation
=
OCRxB
OCFxC
(Int.Req.)
Waveform
Generation
=
OCRxC
( From Analog
Comparator Ouput )
ICFx (Int.Req.)
Edge
Detector
Noise
Canceler
ICRx
ICPx
TCCRxA
TCCRxB
TCCRxC
Note:
Refer to Figure 1 on page 2, Table 30 on page 74, and Table 39 on page 81 for Timer/Counter1
and 3 pin placement and description.
Registers
The Timer/Counter (TCNTn), Output Compare Registers (OCRnA/B/C), and Input Capture Reg-
ister (ICRn) 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 115. The Timer/Counter Control Registers (TCCRnA/B/C) are 8-bit registers and have no
CPU access restrictions. Interrupt requests (shorten as Int.Req.) signals are all visible in the
Timer Interrupt Flag Register (TIFR) and Extended Timer Interrupt Flag Register (ETIFR). All
interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK) and Extended
Timer Interrupt Mask Register (ETIMSK). (E)TIFR and (E)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 Tn 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 ).
n
T
The double buffered Output Compare Registers (OCRnA/B/C) are compared with the
Timer/Counter value at all time. The result of the compare can be used by the waveform gener-
ator to generate a PWM or variable frequency output on the Output Compare Pin (OCnA/B/C).
113
2467P–AVR–08/07
ATMEL [ ATMEL ]
