ATmega8A Atmel Corporation, ATmega8A Datasheet - Page 109

• Manufacturer Part Number: ATmega8A
• Manufacturer: Atmel Corporation

Specifications of ATmega8A

• Flash (kbytes): 8 Kbytes
• Pin Count: 32
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 12
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 23
• Ext Interrupts: 2
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Uart: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 1
• Eeprom (bytes): 512
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 3
• Pwm Channels: 3
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

17.5
8159D–AVR–02/11
Output Compare Unit
Depending on the mode of operation used, the counter is cleared, incremented, or decremented
at each timer clock (clk
selected by the clock select bits (CS22:0). When no clock source is selected (CS22:0 = 0) the
timer is stopped. However, the TCNT2 value can be accessed by the CPU, regardless of
whether clk
count operations.
The counting sequence is determined by the setting of the WGM21 and WGM20 bits located in
the Timer/Counter Control Register (TCCR2). There are close connections between how the
counter behaves (counts) and how waveforms are generated on the Output Compare Output
OC2. For more details about advanced counting sequences and waveform generation, see
“Modes of Operation” on page
The Timer/Counter Overflow (TOV2) Flag is set according to the mode of operation selected by
the WGM21:0 bits. TOV2 can be used for generating a CPU interrupt.
The 8-bit comparator continuously compares TCNT2 with the Output Compare Register
(OCR2). Whenever TCNT2 equals OCR2, the comparator signals a match. A match will set the
Output Compare Flag (OCF2) at the next timer clock cycle. If enabled (OCIE2 = 1), the Output
Compare Flag generates an Output Compare interrupt. The OCF2 Flag is automatically cleared
when the interrupt is executed. Alternatively, the OCF2 Flag can be cleared by software by writ-
ing 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 WGM21:0 bits and Compare Output
mode (COM21:0) bits. The max and bottom signals are used by the waveform generator for han-
dling the special cases of the extreme values in some modes of operation
Operation” on page
Figure 17-3
clk
TOP
BOTTOM
T2
T2
shows a block diagram of the Output Compare unit.
is present or not. A CPU write overrides (has priority over) all counter clear or
112).
T2
). clk
Timer/Counter clock.
Signalizes that TCNT2 has reached maximum value.
Signalizes that TCNT2 has reached minimum value (zero).
112.
T2
can be generated from an external or internal clock source,
ATmega8A
(see “Modes of
109