Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet
Product codes
MEGA328P-XMINI
96
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
Figure 15-2.
Counter Unit Block Diagram
Signal description (internal signals):
count
Increment or decrement TCNT0 by 1.
direction
Select between increment and decrement.
clear
Clear TCNT0 (set all bits to zero).
clk
T
n
Timer/Counter clock, referred to as clk
T0
in the following.
top
Signalize that TCNT0 has reached maximum value.
bottom
Signalize that TCNT0 has reached minimum value (zero).
Depending of the mode of operation used, the counter is cleared, incremented, or decremented at each timer
clock (clk
clock (clk
T0
). clk
T0
can be generated from an external or internal clock source, selected by the Clock Select bits
(CS02:0). When no clock source is selected (CS02:0 = 0) the timer is stopped. However, the TCNT0 value can
be accessed by the CPU, regardless of whether clk
be accessed by the CPU, regardless of whether clk
T0
is present or not. A CPU write overrides (has priority over)
all counter clear or count operations.
The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in the
Timer/Counter Control Register (TCCR0A) and the WGM02 bit located in the Timer/Counter Control Register B
(TCCR0B). There are close connections between how the counter behaves (counts) and how waveforms are
generated on the Output Compare outputs OC0A and OC0B. For more details about advanced counting
sequences and waveform generation, see
Timer/Counter Control Register (TCCR0A) and the WGM02 bit located in the Timer/Counter Control Register B
(TCCR0B). There are close connections between how the counter behaves (counts) and how waveforms are
generated on the Output Compare outputs OC0A and OC0B. For more details about advanced counting
sequences and waveform generation, see
.
The Timer/Counter Overflow Flag (TOV0) is set according to the mode of operation selected by the WGM02:0
bits. TOV0 can be used for generating a CPU interrupt.
bits. TOV0 can be used for generating a CPU interrupt.
15.5
Output Compare Unit
The 8-bit comparator continuously compares TCNT0 with the Output Compare Registers (OCR0A and
OCR0B). Whenever TCNT0 equals OCR0A or OCR0B, the comparator signals a match. A match will set the
Output Compare Flag (OCF0A or OCF0B) at the next timer clock cycle. If the corresponding interrupt is
enabled, the Output Compare Flag generates an Output Compare interrupt. The Output Compare Flag is
automatically cleared when the interrupt is executed. Alternatively, the flag can be cleared by software by writing
a logical one to its I/O bit location. The Waveform Generator uses the match signal to generate an output
according to operating mode set by the WGM02:0 bits and Compare Output mode (COM0x1:0) bits. The max
and bottom signals are used by the Waveform Generator for handling the special cases of the extreme values in
some modes of operation (
OCR0B). Whenever TCNT0 equals OCR0A or OCR0B, the comparator signals a match. A match will set the
Output Compare Flag (OCF0A or OCF0B) at the next timer clock cycle. If the corresponding interrupt is
enabled, the Output Compare Flag generates an Output Compare interrupt. The Output Compare Flag is
automatically cleared when the interrupt is executed. Alternatively, the flag can be cleared by software by writing
a logical one to its I/O bit location. The Waveform Generator uses the match signal to generate an output
according to operating mode set by the WGM02:0 bits and Compare Output mode (COM0x1:0) bits. The max
and bottom signals are used by the Waveform Generator for handling the special cases of the extreme values in
some modes of operation (
).
shows a block diagram of the Output Compare unit.
DATA BUS
TCNTn
Control Logic
count
TOVn
(Int.Req.)
(Int.Req.)
Clock Select
top
Tn
Edge
Detector
( From Prescaler )
clk
Tn
bottom
direction
clear