Datasheet

94
8021G–AVR–03/11
ATmega329P/3290P
14. 8-bit Timer/Counter0 with PWM
14.1 Features
• Single Compare Unit Counter
• Clear Timer on Compare Match (Auto Reload)
• Glitch-free, Phase Correct Pulse Width Modulator (PWM)
• Frequency Generator
• External Event Counter
• 10-bit Clock Prescaler
• Overflow and Compare Match Interrupt Sources (TOV0 and OCF0A)
14.2 Overview
Timer/Counter0 is a general purpose, single compare unit, 8-bit Timer/Counter module. A simpli-
fied block diagram of the 8-bit Timer/Counter is shown in Figure 14-1. For the actual placement
of I/O pins, refer to ”MLF/ Pinout ATmega329P” on page 2 and ”TQFP / Pinout ATmega3290P”
on page 3. 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 ”Register Description” on page
155.
Figure 14-1. 8-bit Timer/Counter Block Diagram
14.2.1 Registers
The Timer/Counter (TCNT0) and Output Compare Register (OCR0A) are 8-bit registers. Inter-
rupt request (abbreviated to Int.Req. in the figure) signals are all visible in the Timer Interrupt
Flag Register (TIFR0). All interrupts are individually masked with the Timer Interrupt Mask Reg-
ister (TIMSK0). TIFR0 and TIMSK0 are not shown in the figure.
The Timer/Counter can be clocked internally, via the prescaler, or by an external clock source on
the T0 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
T0
).
Timer/Counter
DATA BU S
=
TCNTn
Waveform
Generation
OCn
= 0
Control Logic
= 0xFF
BOTTOM
count
clear
direction
TOVn
(Int.Req.)
OCRn
TCCRn
Clock Select
Tn
Edge
Detector
( From Prescaler )
clk
Tn
TOP
OCn
(Int.Req.)