146
7679H–CAN–08/08
AT90CAN32/64/128
Figure 14-1.
8-bit Timer/Counter2 Block Diagram
The Timer/Counter (TCNT2) and Output Compare Register (OCR2A) are 8-bit registers. Inter-
rupt 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 decrement) its value. The Timer/Counter is inac-
tive when no clock source is selected. The output from the Clock Select logic is referred to as the
timer clock (clk
T2
).
The double buffered Output Compare Register (OCR2A) is compared with the Timer/Counter
value at all times. The result of the compare can be used by the Waveform Generator to gener-
ate a PWM or variable frequency output on the Output Compare pin (OC2A).
for details. The compare match event will also set the compare flag
(OCF2A) which can be used to generate an Output Compare interrupt request.
Timer/Counter
DA
T
A
BUS
=
TCNTn
Waveform
Generation
OCnx
= 0
Control Logic
=
0xFF
TOP
BOTTOM
count
clear
direction
TOVn
(Int.Req.)
OCnx
(Int.Req.)
Synchronization Unit
OCRnx
TCCRnx
ASSRn
Status flags
clk
I/O
clk
ASY
Synchronized Status flags
asynchronous mode
select (ASn)
TOSC2
T/C
Oscillator
TOSC1
Prescaler
clk
Tn
clk
I/O
Содержание AVR AT90CAN128
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