Datasheet

Figure 21-1. 16-bit Timer/Counter Block Diagram
(1)
Clock Select
Timer/Counter
DATA BUS
OCRnA
OCRnB
ICRn
=
=
TCNTn
Waveform
Generation
Waveform
Generation
OCnA
OCnB
Noise
Canceler
ICPn
=
Fixed
TOP
Values
Edge
Detector
Control Logic
= 0
TOP BOTTOM
Count
Clear
Direction
TOVn
(Int.Req.)
OCnA
(Int.Req.)
OCnB
(Int.Req.)
ICFn (Int.Req.)
TCCRnA TCCRnB
( From Analog
Comparator Ouput )
Tn
Edge
Detector
( From Prescaler )
clk
Tn
Note: 1. Refer to Pin Configurations, table Port B Pins Alternate Functions in Alternate Functions of Port
B, and table Port D Pins Alternate Functions in Alternate Functions of Port D for Timer/Counter1 pin
placement and description.
Related Links
Pin Configurations
Alternate Functions of Port B
Alternate Functions of Port D
21.2.1 Registers
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 Accessing 16-bit Registers. 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
T1
).
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. The
AVR 8-Bit Microcontroller
16-bit Timer/Counter1
© 2017 Microchip Technology Inc.
Datasheet Complete
40001974A-page 115