Datasheet

109
7766F–AVR–11/10
ATmega16/32U4
Figure 14-1. 16-bit Timer/Counter Block Diagram
(1)
Note: 1. Refer to “Pinout ATmega16U4/ATmega32U4” on page 3, Table 10-3 on page 72, and Table
10-6 on page 75 for Timer/Counter1 and 3 and 3 pin placement and description.
2. Tn only refers to T1 since T3 input is not available on the ATmega16U4/ATmega32U4
product.
14.1.1 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 110. 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 (TIFRn). All interrupts are individually masked with the Timer Inter-
rupt Mask Register (TIMSKn). TIFRn and TIMSKn 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
T
n
).
ICFn (Int.Req.)
TOVn
(Int.Req.)
Clock Select
Timer/Counter
DATABUS
ICRn
=
=
=
TCNTn
Waveform
Generation
Waveform
Generation
Waveform
Generation
OCnA
OCnB
OCnC
Noise
Canceler
ICPn
=
Fixed
TOP
Values
Edge
Detector
Control Logic
= 0
TOP BOTTOM
Count
Clear
Direction
OCFnA
(Int.Req.)
OCFnB
(Int.Req.)
OCFnC
(Int.Req.)
TCCRnA TCCRnB TCCRnC
( From Analog
Comparator Ouput )
Tn
Edge
Detector
( From Prescaler )
TCLK
OCRnC
OCRnB
OCRnA
(2)