Datasheet
95
ATmega169A/PA/329A/PA/649A/P/3290A/PA/6490A/P [DATASHEET]
8284E–AVR–02/2013
15. 8-bit Timer/Counter0 with PWM
15.1 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)
15.2 Overview
Timer/Counter0 is a general purpose, single compare unit, 8-bit Timer/Counter module. A simplified block diagram
of the 8-bit Timer/Counter is shown in Figure 15-1. For the actual placement of I/O pins, refer to Figure 1-2 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 Regis-
ter and bit locations are listed in the ”Register Description” on page 153.
Figure 15-1. 8-bit Timer/Counter block diagram.
15.2.1 Registers
The Timer/Counter (TCNT0) and Output Compare Register (OCR0A) are 8-bit registers. Interrupt request (abbrevi-
ated 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 Register (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
).
The double buffered Output Compare Register (OCR0A) is compared with the Timer/Counter value at all times.
The result of the compare can be used by the Waveform Generator to generate a PWM or variable frequency out-
put on the Output Compare pin (OC0A). See ”Output Compare Unit” on page 98. for details. The compare match
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.)