Rainbow-electronics ATtiny28L Manual de usuario descargar pdf (Pagina 28)

ATtiny28L/V

1062E–10/01

Calibrated Internal

RC Oscillator

The calibrated internal oscillator provides a fixed 1.2 MHz (nominal) clock at 3V and

°C. This clock may be used as the system clock. See the section “Clock Options” on

page 4 for information on how to select this clock as the system clock. This oscillator

can be calibrated by writing the calibration byte to the OSCCAL register. When this

oscillator is used as the chip clock, the Watchdog oscillator will still be used for the

Watchdog Timer and for the reset time-out. For details on how to use the pre-pro-

grammed calibration value, see the section “Calibration Byte” on page 44.

Oscillator Calibration Register

– OSCCAL

• Bits 7..0 – CAL7..CAL0: Oscillator Calibration Value

Writing the calibration byte to this address will trim the internal oscillator to remove pro-

cess variation from the oscillator frequency. When OSCCAL is zero, the lowest available

frequency is chosen. Writing non-zero values to the register will increase the frequency

to the internal oscillator. Writing $FF to the register gives the highest available fre-

quency. Table 12 shows the range for OSCCAL. Note that the oscillator is intended for

calibration to 1.2 MHz, thus tuning to other values is not guaranteed. At 3V and 25

the pre-programmed calibration byte gives a frequency within ± 1% of the nominal

frequency.

Bit 76543210

$00 CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value 0 0 0 0 0 0 0 0

Table 12. Internal RC Oscillator Range

OSCCAL Value Min Frequency Max Frequency

0x00 0.6 MHz 1.2 MHz

0x7F 0.8 MHz 1.7 MHz

0xFF 1.2 MHz 2.5 MHz

1 2 ... 23 24 25 26 27 28 29 30 31 32 33 ... 74 75

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Rainbow-electronics ATtiny28L Manual de usuario Pagina 28