ATmega16HVB datasheet(26/273 Pages) ATMEL

26 / 273 page

8042A–AVR–07/09

ATmega16HVB/32HVB

9.1.4

Voltage ADC Clock – clk

VADC

The Voltage ADC is provided with a dedicated clock domain. The VADC clock is automatically

prescaled relative to the System Clock Prescalers setting by the VADC Prescaler, giving a fixed

VADC clock at 1 MHz.

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 describes the clock sources available in the device. The clocks are input to

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

The ATmega16HVB/32HVB has 3 on-board oscillator used to clock the internal logic. Table 9-1

shows the clock sources and their usage.

9.2.1

Calibrated Fast RC Oscillator

The calibrated Fast RC Oscillator by default provides a 8.0 MHz clock. The frequency is nominal

value at 25

°C. This clock will operate with no external components. During reset, hardware

loads the calibration byte into the FOSCCAL Register and thereby automatically calibrates the

Fast RC Oscillator. At 25

°C, this calibration gives a frequency of 8 MHz ± 1%. The oscillator can

be calibrated to any frequency in the range 7.3 - 8.1 MHz by changing the FOSCCAL register.

For more information on the pre-programmed calibration value, see the section ”Reading the

Signature Row from Software” on page 199. Note that the frequency of the system clock is given

by the ”System Clock Prescaler” on page 28.

Table 9-1.

Available Clock Sources.

Clock Source

Usage

Calibrated Fast RC Oscillator

The clock source for the CPU, I/O, Flash, and Voltage ADC.

Ultra Low Power RC Oscillator

The clock source for the Watchdog Timer, Battery Protection,

Coulomb Counter ADC, Bandgap Buffer Short Circuit Detector,

and SMBus Connect/Disconnect.

Slow RC Oscillator

Used by the Oscillator Sampling Interface (OSI).

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