AT90SCR100 datasheet(37/433 Pages) ATMEL

37 / 433 page

TPR0327AY–SMS–30Jan09

AT90SCR100

Figure 7-4.

Programming PLL

7.2.5

Internal RC Oscillator

By default, the Internal RC Oscillator provides an approximate 8 MHz clock. Though voltage and

temperature dependent, this clock can be very accurately calibrated by the user. See Table 31-2

on page 411 and “Internal RC Oscillator Speed” on page 38 for more details.

This oscillator is used to time Eeprom and Flash write accesses. This is why its calibration is

important.

During reset, hardware loads the pre-programmed calibration value into the OSCCAL Register

and thereby automatically calibrates the RC Oscillator. The accuracy of this calibration is shown

as Factory calibration in Table 31-2 on page 411.

By changing the OSCCAL register from SW, see “OSCCAL – Oscillator Calibration Register” on

page 39, it is possible to get a higher calibration accuracy than by using the factory calibration.

The accuracy of this calibration is shown as User calibration in Table 31-2 on page 411.

Switch clk

to clk

PLLCR.PLLMUX = 1

MUX

PLL

Configure CPU Divider

CLKPR = xxxxb

Enable PLL

PLLCR.ON = 1

Yes

Is PLL Locked ?

PLLCR.LOCK = 1 ?

PLL Programming

AT90SCR100 数据表(PDF) 37 Page - ATMEL Corporation