ATmega8 Atmel Corporation, ATmega8 Datasheet - Page 49

• 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

Moving Interrupts
Between Application
and Boot Space
General Interrupt
Control Register –
GICR
2486Z–AVR–02/11
When the BOOTRST Fuse is programmed, the boot section size set to 2Kbytes, and the IVSEL
bit in the GICR Register is set before any interrupts are enabled, the most typical and general
program setup for the Reset and Interrupt Vector Addresses is:
The General Interrupt Control Register controls the placement of the Interrupt Vector table.
• Bit 1 – IVSEL: Interrupt Vector Select
When the IVSEL bit is cleared (zero), the Interrupt Vectors are placed at the start of the Flash
memory. When this bit is set (one), the Interrupt Vectors are moved to the beginning of the Boot
Loader section of the Flash. The actual address of the start of the boot Flash section is deter-
mined by the BOOTSZ Fuses. Refer to the section
Self-Programming” on page 202
tables, a special write procedure must be followed to change the IVSEL bit:
1. Write the Interrupt Vector Change Enable (IVCE) bit to one
2. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE
Interrupts will automatically be disabled while this sequence is executed. Interrupts are disabled
in the cycle IVCE is set, and they remain disabled until after the instruction following the write to
IVSEL. If IVSEL is not written, interrupts remain disabled for four cycles. The I-bit in the Status
Register is unaffected by the automatic disabling.
Note: If Interrupt Vectors are placed in the Boot Loader section and Boot Lock bit BLB02 is pro-
grammed, interrupts are disabled while executing from the Application section. If Interrupt
Vectors are placed in the Application section and Boot Lock bit BLB12 is programed, interrupts
are disabled while executing from the Boot Loader section. Refer to the section
Support – Read-While-Write Self-Programming” on page 202
Bit
Read/Write
Initial Value
AddressLabels
;
.org $c00
$c00
$c01
$c02
...
$c12
$c13
$c14
$c15
$c16
$c17
$c18
RESET: ldi
INT1
R/W
7
0
rjmp
rjmp
rjmp
...
rjmp
out
ldi
out
sei
<instr>
INT0
R/W
6
0
Code
RESET
EXT_INT0
EXT_INT1
... ;
SPM_RDY
SPH,r16
r16,low(RAMEND)
SPL,r16
xxx
r16,high(RAMEND); Main program start
R
5
–
0
for details. To avoid unintentional changes of Interrupt Vector
R
4
–
0
Comments
; Reset handler
; IRQ0 Handler
; IRQ1 Handler
; Store Program Memory Ready Handler
; Set Stack Pointer to top of RAM
; Enable interrupts
R
3
–
0
“Boot Loader Support – Read-While-Write
R
2
–
0
for details on Boot Lock Bits.
IVSEL
R/W
1
0
ATmega8(L)
IVCE
R/W
0
0
GICR
“Boot Loader
49