Datasheet

8024A–AVR–04/08

ATmega8HVA/16HVA

9.1.5 Coulomb Counter ADC Clock - clk

CCADC

The Coulomb Counter ADC is provided with a dedicated clock domain. This allows operating the

Coulomb Counter ADC in low power modes like Power-save for continuous current

measurements.

9.1.6 Watchdog Timer and Battery Protection Clock

The Watchdog Timer and Battery Protection are provided with a dedicated clock domain. This

allows operation in all modes except Power-off. It also allows very low power operation by utiliz-

ing an Ultra Low Power RC Oscillator dedicated to this purpose.

9.2 Clock Sources

The following section describe the clock sources available in the device. The clocks are input to

the AVR clock generator, and routed to the appropriate modules.

9.3 Calibrated Fast RC Oscillator

The calibrated Fast RC Oscillator by default provides a 8.0 MHz clock to the system clock pres-

caler. The frequency is nominal value at 70°C. This clock will operate with no external

components. With an accurate time reference and by using runtime calibration, this oscillator

can be calibrated to an accuracy of +/- 1. % over the entire temperature range. During reset,

hardware loads the calibration byte into the FOSCCAL Register and thereby automatically cali-

brates the Fast RC Oscillator. At 70°C, this calibration gives a frequency of 8 MHz ± 4%. The

oscillator can be calibrated to any frequency in the range 7.3- 8.1 MHz by changing the FOSC-

CAL register. For more information on the pre-programmed calibration value, see the section

”Reading the Signature Row from Software” on page 144. Note that the frequency of the system

clock is given by the ”System Clock Prescaler” on page 27.

Start-up time of the chip is referred to as a number of Prescaled Fast RC Oscillator cycles (CK)

and a number of ULP oscillator cycles. The start-up time is selected by SUT fuses as defined in

Table 9-1 on page 25.

Notes: 1. The device is shipped with this option selected.

2. The actual value of the added, selectable 4- 512 ms delay depends on the actual frequency of

the “Ultra Low Power RC Oscillator”. See Table 9-2 on page 27 and ”Electrical Characteristics”

on page 165

Table 9-1. Start-up times according to SUT fuse selection.

SUT3..0

Start-up Time from

Power-save Additional Delay from Reset, Typical Values

(2)

000 6 CK 14 CK + 4 ms

001 6 CK 14 CK + 8 ms

010 6 CK 14 CK + 16 ms

011 6 CK 14 CK + 32 ms

100 6 CK 14 CK + 64 ms

101 6 CK 14 CK + 128 ms

110 6 CK 14 CK + 256 ms

111

(1)

6 CK 14 CK + 512 ms