Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet
Product codes
MEGA328P-XMINI
154
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
are disconnected from Port B. A crystal can then be connected between the TOSC1 and TOSC2 pins to serve
as an independent clock source for Timer/Counter2. The Oscillator is optimized for use with a 32.768kHz
crystal.
as an independent clock source for Timer/Counter2. The Oscillator is optimized for use with a 32.768kHz
crystal.
For Timer/Counter2, the possible prescaled selections are: clk
T2S
/8, clk
T2S
/32, clk
T2S
/64, clk
T2S
/128, clk
T2S
/256,
and clk
T2S
/1024. Additionally, clk
T2S
as well as 0 (stop) may be selected. Setting the PSRASY bit in GTCCR
resets the prescaler. This allows the user to operate with a predictable prescaler.
18.11 Register Description
18.11.1 TCCR2A – Timer/Counter Control Register A
• Bits 7:6 – COM2A1:0: Compare Match Output A Mode
These bits control the Output Compare pin (OC2A) behavior. If one or both of the COM2A1:0 bits are set, the
OC2A output overrides the normal port functionality of the I/O pin it is connected to. However, note that the Data
Direction Register (DDR) bit corresponding to the OC2A pin must be set in order to enable the output driver.
OC2A output overrides the normal port functionality of the I/O pin it is connected to. However, note that the Data
Direction Register (DDR) bit corresponding to the OC2A pin must be set in order to enable the output driver.
When OC2A is connected to the pin, the function of the COM2A1:0 bits depends on the WGM22:0 bit setting.
shows the COM2A1:0 bit functionality when the WGM22:0 bits are set to a normal or CTC mode
(non-PWM).
Note:
1.
A special case occurs when OCR2A equals TOP and COM2A1 is set. In this case, the Compare Match is
ignored, but the set or clear is done at BOTTOM. See
ignored, but the set or clear is done at BOTTOM. See
Bit
7
6
5
4
3
2
1
0
COM2A1
COM2A0
COM2B1
COM2B0
–
–
WGM21
WGM20
TCCR2A
Read/Write
R/W
R/W
R/W
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Table 18-2.
Compare Output Mode, non-PWM Mode
COM2A1
COM2A0
Description
0
0
Normal port operation, OC0A disconnected.
0
1
Toggle OC2A on Compare Match
1
0
Clear OC2A on Compare Match
1
1
Set OC2A on Compare Match
Table 18-3.
Compare Output Mode, Fast PWM Mode
COM2A1
COM2A0
Description
0
0
Normal port operation, OC2A disconnected.
0
1
WGM22 = 0: Normal Port Operation, OC0A Disconnected.
WGM22 = 1: Toggle OC2A on Compare Match.
WGM22 = 1: Toggle OC2A on Compare Match.
1
0
Clear OC2A on Compare Match, set OC2A at BOTTOM,
(non-inverting mode).
(non-inverting mode).
1
1
Set OC2A on Compare Match, clear OC2A at BOTTOM,
(inverting mode).
(inverting mode).