8-bit Timer/Counter2 Timer/Counter2 is a general purpose, single compare unit, 8-bit Timer/Counter module.
The main features are:
• Single Compare unit Counter
• Clear Timer on Compare Match (Auto Reload)
• Glitch-free, Phase Correct Pulse Width Modulator (PWM)
with PWM and
Asynchronous
Operation
• Frequency Generator
• 10-bit Clock Prescaler
• Overflow and Compare Match Interrupt Sources (TOV2 and OCF2)
• Allows clocking from External 32 kHz Watch Crystal Independent of the I/O Clock
Overview
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 53. For the
actual placement of I/O pins, refer to “Pinout ATmega32” on page 2. CPU accessible I/O
Registers, including I/O bits and I/O pins, are shown in bold. The device-specific I/O
Register and bit locations are listed in the “8-bit Timer/Counter Register Description” on
page 125.
Figure 53. 8-bit Timer/Counter Block Diagram
TCCRn
count
TOVn
(Int.Req.)
clear
Control Logic
TOP
direction
clkTn
TOSC1
TOSC2
BOTTOM
T/C
Oscillator
Prescaler
Timer/Counter
TCNTn
= 0
= 0xFF
clkI/O
OCn
OCn
(Int.Req.)
Waveform
Generation
=
OCRn
clkI/O
Synchronized Status flags
Synchronization Unit
clkASY
Status flags
ASSRn
asynchronous mode
select (ASn)
Registers
The Timer/Counter (TCNT2) and Output Compare Register (OCR2) are 8-bit registers.
Interrupt request (shorten as Int.Req.) 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 asynchronously
clocked from the TOSC1/2 pins, as detailed later in this section. The asynchronous
operation is controlled by the Asynchronous Status Register (ASSR). The Clock Select
logic block controls which clock source the Timer/Counter uses to increment (or decre-
ment) 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 (clkT2).
114
ATmega32(L)
2503J–AVR–10/06
ATMEL [ ATMEL ]
