ATmega8HVA Atmel Corporation, ATmega8HVA Datasheet - Page 119

• Manufacturer Part Number: ATmega8HVA
• Manufacturer: Atmel Corporation

Specifications of ATmega8HVA

• Flash (kbytes): 8 Kbytes
• Pin Count: 28
• Max. Operating Frequency: 4 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 3
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 6
• Ext Interrupts: 3
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 6
• Adc Resolution (bits): 12
• Adc Speed (ksps): 1.9
• Resistive Touch Screen: No
• Temp. Sensor: Yes
• Crypto Engine: No
• Sram (kbytes): 0.5
• Eeprom (bytes): 256
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -20 to 85
• I/o Supply Class: 1.8 to 9.0
• Operating Voltage (vcc): 1.8 to 9.0
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 2
• Output Compare Channels: 4
• Input Capture Channels: 2
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

21.3.2
8024A–AVR–04/08
BGCRR – Bandgap Calibration R Register
• Bit 7:0 – BGCR7:0: BG Calibration of Resistor ladder
These bits are used for temperature gradient adjustment of the bandgap reference.
illustrates VREF as a function of temperature. VREF has a positive temperature coefficient at
low temperatures and negative temperature coefficient at high temperatures. Depending on the
process variations, the top of the VREF curve may be located at higher or lower temperatures.
To minimize the temperature drift in the temperature range of interest, BGCRR is used to adjust
the top of the curve towards the centre of the temperature range of interest. The BGCRR bits are
thermometer coded, resulting in 9 possible settings: 00000000, 00000001, 00000011,
00000111, … , 11111111. The value 00000000 shifts the top of the VREF curve to the highest
possible temperature, and the value 11111111 shifts the top of the VREF curve to the lowest
possible temperature.
Figure 21-2. Illustration of VREF as a function of temperature.
Bit
(0xD1)
Read/Write
Initial Value
1.5
0.5
1
0
-40
BGCR7
R/W
-20
7
0
BGCR6
R/W
6
0
0
BGCR5
R/W
5
0
Temperature range of interest
20
Temperature [
BGCR4
R/W
4
0
o
C]
40
BGCRR is used to move the top of the VREF
curve to the center of the tempearture range of
interest.
BGCR3
R/W
3
1
ATmega8HVA/16HVA
BGCR2
60
R/W
1
2
BGCR1
R/W
1
1
80
BGCR0
R/W
0
1
100
Figure 21-2
BGCRR
119