ATmega8HVA Atmel Corporation, ATmega8HVA Datasheet - Page 29

• 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

9.12.3
8024A–AVR–04/08
Usage
Figure 9-2.
Note:
The osi_posedge signal pulses on each rising edge of the prescaled Slow RC/ ULP oscillator
clock. This signal is not directly accessible by the CPU, but can be used to trigger the input cap-
ture function of Timer/Counter0. Using OSI in combination with the input capture function of
Timer/Counter0 facilitates accurate measurement of the oscillator frequencies with a minimum
of CPU calculation. Refer to
enable the Input Capture function.
The Slow RC oscillator represents a highly predictable and accurate clock source over the entire
temperature range and provides an excellent reference for calibrating the Fast RC oscillator
runtime. Typically, runtime calibration is needed to provide an accurate Fast RC frequency for
asynchronous serial communication in the complete temperature range. An accurate time refer-
ence is also needed to calculate accumulated charge during a CC-ADC measurement.
The Slow RC frequency at T
cient are stored in the signature row. The value of T
characteristics can be used to calculate the actual Slow RC clock period at a given temperature
with high precision. Refer to
By measuring the number of CPU cycles of one or more prescaled Slow RC clock periods, the
actual Fast RC oscillator clock period can be determined. The Fast RC clock period can then be
adjusted by writing to the FOSCCAL register. The new Fast RC clock period after calibration
should be verified by repeating the measurement and repeating the calibration if necessary. The
Fast RC clock period as a function of the Slow RC clock period is given by:
where n is the number of prescaled Slow RC periods that is used in the measurement. Using
more prescaled Slow RC periods decreases the measurement error, but increases the time con-
sumed for calibration. Note that the Slow RC Oscillator needs very short time to stabilize after
1. One prescaled Slow RC/ULP oscillator period corresponds to 128 times the actual Slow
RC/ULP oscillator period.
Power RC
Ultra Low
Oscillator
Oscillator
Slow RC
T
Oscillator Sampling Interface Block Diagram
FastRC
=
T
SlowRC
”Slow RC Oscillator” on page 26
OSISEL0
HOT
”Timer/Counter(T/C0,T/C1)” on page 77
⋅
------------------------------------------------------------------------------------------------------------------------------------------------ -
number of CPU cycles in n prescaled Slow RC periods
(calibration temperature) and the Slow RC temperature coeffi-
7 bit prescaler
Databus
OSICSR
HOT
128 n ⋅
ATmega8HVA/16HVA
is also stored in the signature row. These
(1)
for details.
Detector
Oscillator
Fast RC
Edge
for details on how to
osi_posedge
29