ATMEGA325-16AJ ATMEL [ATMEL Corporation], ATMEGA325-16AJ Datasheet - Page 124

• Manufacturer Part Number: ATMEGA325-16AJ
• Description: 8-bit Microcontroller with In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

8-bit Timer/Counter2
with PWM and
Asynchronous
Operation
Overview
Registers
124
ATmega325/3250/645/6450
Timer/Counter2 is a general purpose, single compare unit, 8-bit Timer/Counter module.
The main features are:
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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 ATmega3250/6450” 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 135.
Figure 53. 8-bit Timer/Counter Block Diagram
The Timer/Counter (TCNT2) and Output Compare Register (OCR2A) are 8-bit registers.
Interrupt request (shorten as Int.Req.) signals are all visible in the Timer Interrupt Flag
Register (TIFR2). All interrupts are individually masked with the Timer Interrupt Mask
Register (TIMSK2). TIFR2 and TIMSK2 are not shown in the figure.
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-
Single Compare Unit Counter
Clear Timer on Compare Match (Auto Reload)
Glitch-free, Phase Correct Pulse Width Modulator (PWM)
Frequency Generator
10-bit Clock Prescaler
Overflow and Compare Match Interrupt Sources (TOV2 and OCF2A)
Allows Clocking from External 32 kHz Watch Crystal Independent of the I/O Clock
Status flags
Timer/Counter
TCNTn
OCRnx
=
ASSRn
direction
count
clear
BOTTOM
Synchronized Status flags
= 0
Control Logic
=
TCCRnx
TOP
asynchronous mode
0xFF
select (ASn)
clk
Tn
Synchronization Unit
OCnx
(Int.Req.)
Generation
Prescaler
Waveform
Oscillator
T/C
OCnx
clk
2570A–AVR–09/04
TOVn
(Int.Req.)
clk
clk
ASY
I/O
I/O
TOSC1
TOSC2