ATMEGA8A-AUR Atmel, ATMEGA8A-AUR Datasheet - Page 30

• Manufacturer Part Number: ATMEGA8A-AUR
• Description: MCU AVR 8KB FLASH 16MHZ 32TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA8A-AUR

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 16MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 23
• Program Memory Size: 8KB (4K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 512 x 8
• Ram Size: 1K x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

8.7
8.8
8159D–AVR–02/11
External Clock
Timer/Counter Oscillator
To drive the device from an external clock source, XTAL1 should be driven as shown in
8-4. To run the device on an external clock, the CKSEL Fuses must be programmed to “0000”.
By programming the CKOPT Fuse, the user can enable an internal 36 pF capacitor between
XTAL1 and GND, and XTAL2 and GND.
Figure 8-4.
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table
Table 8-10.
When applying an external clock, it is required to avoid sudden changes in the applied clock fre-
quency to ensure stable operation of the MCU. A variation in frequency of more than 2% from
one clock cycle to the next can lead to unpredictable behavior. It is required to ensure that the
MCU is kept in Reset during such changes in the clock frequency.
For AVR microcontrollers with Timer/Counter Oscillator pins (TOSC1 and TOSC2), the crystal is
connected directly between the pins. By programming the CKOPT Fuse, the user can enable
internal capacitors on XTAL1 and XTAL2, thereby removing the need for external capacitors.
The Oscillator is optimized for use with a 32.768 kHz watch crystal. Applying an external clock
source to TOSC1 is not recommended.
Note:
SUT1:0
00
01
10
11
8-10.
The Timer/Counter Oscillator uses the same type of crystal oscillator as Low-Frequency Oscillator
and the internal capacitors have the same nominal value of 36 pF.
External Clock Drive Configuration
Start-up Times for the External Clock Selection
Start-up Time from
Power-down and
Power-save
6 CK
6 CK
6 CK
EXTERNAL
SIGNAL
CLOCK
Additional Delay
(V
from Reset
CC
4.1 ms
Reserved
65 ms
= 5.0V)
–
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
ATmega8A
Figure
30