Rainbow Electronics ATtiny2313 - Manual (Page 64)

64
ATtiny2313
2543A–AVR–08/03
8-bit Timer/Counter0
with PWM
Timer/Counter0 is a general purpose 8-bit Timer/Counter module, with two independent
Output Compare Units, and with PWM support. It allows accurate program execution
timing (event management) and wave generation. The main features are:
•
Two Independent Output Compare Units
• Double Buffered Output Compare Registers
• Clear Timer on Compare Match (Auto Reload)
• Glitch Free, Phase Correct Pulse Width Modulator (PWM)
• Variable PWM Period
• Frequency Generator
• Three Independent Interrupt Sources (TOV0, OCF0A, and OCF0B)
Overview A simplified block diagram of the 8-bit Timer/Counter is shown in Figure 26. For the
actual placement of I/O pins, refer to “Pinout ATtiny2313” on page 1. 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 75.
Figure 26. 8-bit Timer/Counter Block Diagram
Registers The Timer/Counter (TCNT0) and Output Compare Registers (OCR0A and OCR0B) are
8-bit registers. Interrupt request (abbreviated to Int.Req. in the figure) signals are all vis-
ible 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.
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 Registers (OCR0A and OCR0B) 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 output on the Output
Clock Select
Timer/Counter
DA
T
A
B
U
S
OCRnA
OCRnB
=
=
TCNTn
Waveform
Generation
Waveform
Generation
OCnA
OCnB
=
Fixed
TOP
Value
Control Logic
= 0
TOP BOTTOM
Count
Clear
Direction
TOVn
(Int.Req.)
OCnA
(Int.Req.)
OCnB
(Int.Req.)
TCCRnA TCCRnB
Tn
Edge
Detector
( From Prescaler )
clk
Tn