ATmega8 Atmel Corporation, ATmega8 Datasheet - Page 66

• 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

External
Interrupts
MCU Control Register
– MCUCR
66
ATmega8(L)
The external interrupts are triggered by the INT0, and INT1 pins. Observe that, if enabled, the
interrupts will trigger even if the INT0..1 pins are configured as outputs. This feature provides a
way of generating a software interrupt. The external interrupts can be triggered by a falling or ris-
ing edge or a low level. This is set up as indicated in the specification for the MCU Control
Register – MCUCR. When the external interrupt is enabled and is configured as level triggered,
the interrupt will trigger as long as the pin is held low. Note that recognition of falling or rising
edge interrupts on INT0 and INT1 requires the presence of an I/O clock, described in
Systems and their Distribution” on page
asynchronously. This implies that these interrupts can be used for waking the part also from
sleep modes other than Idle mode. The I/O clock is halted in all sleep modes except Idle mode.
Note that if a level triggered interrupt is used for wake-up from Power-down mode, the changed
level must be held for some time to wake up the MCU. This makes the MCU less sensitive to
noise. The changed level is sampled twice by the Watchdog Oscillator clock. The period of the
Watchdog Oscillator is 1 µs (nominal) at 5.0V and 25°C. The frequency of the Watchdog Oscilla-
tor is voltage dependent as shown in
wake up if the input has the required level during this sampling or if it is held until the end of the
start-up time. The start-up time is defined by the SUT Fuses as described in
Clock Options” on page
disappears before the end of the start-up time, the MCU will still wake up, but no interrupt will be
generated. The required level must be held long enough for the MCU to complete the wake up to
trigger the level interrupt.
The MCU Control Register contains control bits for interrupt sense control and general MCU
functions.
• Bit 3, 2 – ISC11, ISC10: Interrupt Sense Control 1 Bit 1 and Bit 0
The External Interrupt 1 is activated by the external pin INT1 if the SREG I-bit and the corre-
sponding interrupt mask in the GICR are set. The level and edges on the external INT1 pin that
activate the interrupt are defined in
detecting edges. If edge or toggle interrupt is selected, pulses that last longer than one clock
period will generate an interrupt. Shorter pulses are not guaranteed to generate an interrupt. If
low level interrupt is selected, the low level must be held until the completion of the currently
executing instruction to generate an interrupt.
Table 31. Interrupt 1 Sense Control
Bit
Read/Write
Initial Value
ISC11
0
0
1
1
ISC10
0
1
0
1
R/W
SE
7
0
Description
The low level of INT1 generates an interrupt request
Any logical change on INT1 generates an interrupt request
The falling edge of INT1 generates an interrupt request
The rising edge of INT1 generates an interrupt request
SM2
R/W
6
0
25. If the level is sampled twice by the Watchdog Oscillator clock but
SM1
R/W
5
0
Table
“Electrical Characteristics” on page
SM0
R/W
0
4
25. Low level interrupts on INT0/INT1 are detected
31. The value on the INT1 pin is sampled before
ISC11
R/W
3
0
ISC10
R/W
2
0
ISC01
R/W
1
0
ISC00
R/W
0
0
235. The MCU will
“System Clock and
MCUCR
2486Z–AVR–02/11
“Clock