8-bit Timer/Counter0 with PWM
Timer/Counter0 is a general purpose, single channel, 8-bit Timer/Counter module. The
main features are:
Features
Overview
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Single Channel 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)
Many register and bit references in this section are written in general form.
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A lower case “n” replaces the Timer/Counter number, in this case 0. 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.
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A lower case “x” replaces the Output Compare unit channel, in this case A.
However, when using the register or bit defines in a program, the precise form must
be used, i.e., OCR0A for accessing Timer/Counter0 output compare channel A
value and so on.
A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 37. For the
actual placement of I/O pins, refer to “Pinout AT90CAN128- TQFP” on page 4. 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 104.
Figure 37. 8-bit Timer/Counter Block Diagram
TCCRn
count
TOVn
(Int.Req.)
clear
Control Logic
TOP
Clock Select
direction
clk
Tn
Edge
Detector
Tn
BOTTOM
( From Prescaler )
Timer/Counter
TCNTn
= 0
= 0xFF
OCn
(Int.Req.)
Waveform
Generation
OCnx
=
OCRnx
Registers
The Timer/Counter (TCNT0) and Output Compare Register (OCR0A) are 8-bit registers.
Interrupt request (abbreviated to Int.Req. in the figure) signals are all visible in the Timer
94
AT90CAN128
4250E–CAN–12/04
ATMEL [ ATMEL ]
