ATmega8 Atmel Corporation, ATmega8 Datasheet - Page 99

• Manufacturer Part Number: ATmega8
• Manufacturer: Atmel Corporation

Specifications of ATmega8

• 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
• Output Compare Channels: 3
• Input Capture Channels: 1
• Pwm Channels: 3
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

Timer/Counter 1 –
TCNT1H and TCNT1L
Output Compare
Register 1 A –
OCR1AH and OCR1AL
Output Compare
Register 1 B –
OCR1BH and OCR1BL
2486Z–AVR–02/11
Table 40. Clock Select Bit Description
If external pin modes are used for the Timer/Counter1, transitions on the T1 pin will clock the
counter even if the pin is configured as an output. This feature allows software control of the
counting.
The two Timer/Counter I/O locations (TCNT1H and TCNT1L, combined TCNT1) give direct
access, both for read and for write operations, to the Timer/Counter unit 16-bit counter. To
ensure that both the high and Low bytes are read and written simultaneously when the CPU
accesses these registers, the access is performed using an 8-bit temporary High byte Register
(TEMP). This temporary register is shared by all the other 16-bit registers.
Registers” on page 77.
Modifying the counter (TCNT1) while the counter is running introduces a risk of missing a Com-
pare Match between TCNT1 and one of the OCR1x Registers.
Writing to the TCNT1 Register blocks (removes) the Compare Match on the following timer clock
for all compare units.
Bit
Read/Write
Initial Value
Bit
Read/Write
Initial Value
Bit
Read/Write
Initial Value
CS12
0
0
0
0
1
1
1
1
CS11
0
0
1
1
0
0
1
1
R/W
R/W
R/W
7
0
7
0
7
0
CS10
0
1
0
1
0
1
0
1
R/W
R/W
R/W
6
0
6
0
6
0
Description
No clock source. (Timer/Counter stopped)
clk
clk
clk
clk
clk
External clock source on T1 pin. Clock on falling edge
External clock source on T1 pin. Clock on rising edge
R/W
R/W
R/W
I/O
I/O
I/O
I/O
I/O
5
0
5
0
5
0
/1 (No prescaling)
/8 (From prescaler)
/64 (From prescaler)
/256 (From prescaler)
/1024 (From prescaler)
R/W
R/W
R/W
OCR1A[15:8]
OCR1B[15:8]
4
TCNT1[15:8]
0
4
0
4
0
OCR1A[7:0]
OCR1B[7:0]
TCNT1[7:0]
R/W
R/W
R/W
3
0
3
0
3
0
R/W
R/W
R/W
2
0
2
0
2
0
R/W
R/W
R/W
1
0
1
0
1
0
R/W
R/W
R/W
ATmega8(L)
0
0
0
0
0
0
See “Accessing 16-bit
OCR1AH
OCR1BH
OCR1AL
OCR1BL
TCNT1H
TCNT1L
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