atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 90

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

13.1.2
13.2
13.3
90
Timer/Counter Clock Sources
Counter Unit
ATmega32U4
Definitions
The double buffered Output Compare Registers (OCR0A and OCR0B) are compared with the
Timer/Counter value at all times. The result of the compare can be used by the Waveform Gen-
erator to generate a PWM or variable frequency output on the Output Compare pins (OC0A and
OC0B).
set the Compare Flag (OCF0A or OCF0B) which can be used to generate an Output Compare
interrupt request.
Many register and bit references in this section are written in general form. A lower case “n”
replaces the Timer/Counter number, in this case 0. A lower case “x” replaces the Output Com-
pare Unit, in this case Compare Unit A or Compare Unit B. However, when using the register or
bit defines in a program, the precise form must be used, i.e., TCNT0 for accessing
Timer/Counter0 counter value and so on.
The definitions in the table below are also used extensively throughout the document.
The Timer/Counter can be clocked by an internal or an external clock source. The clock source
is selected by the Clock Select logic which is controlled by the Clock Select (CS02:0) bits
located in the Timer/Counter Control Register (TCCR0B). For details on clock sources and pres-
caler, see
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit.
13-2
Figure 13-2. Counter Unit Block Diagram
Signal description (internal signals):
BOTTOM
MAX
TOP
shows a block diagram of the counter and its surroundings.
count
direction
clear
See “Output Compare Unit” on page 91.
“Timer/Counter0, Timer/Counter1, and Timer/Counter3 Prescalers” on page
The counter reaches the BOTTOM when it becomes 0x00.
The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
The counter reaches the TOP when it becomes equal to the highest
value in the count sequence. The TOP value can be assigned to be the
fixed value 0xFF (MAX) or the value stored in the OCR0A Register. The
assignment is dependent on the mode of operation.
DATA BUS
TCNTn
Increment or decrement TCNT0 by 1.
Select between increment and decrement.
Clear TCNT0 (set all bits to zero).
direction
count
clear
bottom
Control Logic
for details. The Compare Match event will also
top
TOVn
(Int.Req.)
clk
Tn
Clock Select
( From Prescaler )
Detector
Edge
7766A–AVR–03/08
Tn
87.
Figure