AT90SCR100 datasheet(39/433 Pages) ATMEL

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TPR0327AY–SMS–30Jan09

AT90SCR100

7.2.5.2

OSCCAL – Oscillator Calibration Register

• Bits 7:0 – CAL7:0: Oscillator Calibration Value

The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to

remove process variations from the oscillator frequency. A pre-programmed calibration value is

automatically written to this register during chip reset, giving the Factory calibrated frequency as

specified in Table 31-2 on page 411. The application software can write this register to change

the oscillator frequency. The oscillator can be calibrated to frequencies as specified in Table 31-

2 on page 411. Calibration outside that range is not guaranteed.

Note that this oscillator is used to time EEPROM and Flash write accesses, and these write

times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more

than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail.

The CAL7 bit determines the range of operation for the oscillator. Setting this bit to 0 gives the

lowest frequency range, setting this bit to 1 gives the highest frequency range. The two fre-

quency ranges are overlapping, in other words a setting of OSCCAL = 0x7F gives a higher

frequency than OSCCAL = 0x80.

The CAL6..0 bits are used to tune the frequency within the selected range. A setting of 0x00

gives the lowest frequency in that range, and a setting of 0x7F gives the highest frequency in the

range.

7.2.6

RTC Clock

AT90SCR100 supports a RTC counting feature by using Timer 2. The description of the Real

Time Counter is described Section 13.3 “8-bit Timer/Counter2 with PWM and Asynchronous

Operation (RTC)” on page 134.

The external clock to connect to get a accurate RTC is a 32.768 KHz clock.

Figure 7-7.

RTC Clock Connection

Bit

7654

$000066

CAL7

CAL6

CAL5

CAL4

CAL3

CAL2

CAL1

CAL0

OSCCAL

Read/write

R/W

Initial value

Device Specific Calibration Value

TOSC1

C1 = 22pF

C2 = 22pF

TOSC2

32.768 KHz

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