ATmega16 datasheet(28/315 Pages) ATMEL

28 / 315 page

ATmega16(L)

2466E–AVR–10/02

When this Oscillator is selected, start-up times are determined by the SUT fuses as

shown in Table 10. XTAL1 and XTAL2 should be left unconnected (NC).

Note:

1. The device is shipped with this option selected.

Oscillator Calibration Register

– OSCCAL

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

Writing the calibration byte to this address will trim the Internal Oscillator to remove pro-

cess variations from the Oscillator frequency. This is done automatically during Chip

Reset. When OSCCAL is zero, the lowest available frequency is chosen. Writing non-

zero values to this register will increase the frequency of the Internal Oscillator. Writing

$FF to the register gives the highest available frequency. The calibrated Oscillator is

used to time EEPROM and Flash access. If EEPROM or Flash is written, do not cali-

brate to more than 10% above the nominal frequency. Otherwise, the EEPROM or Flash

write may fail. Note that the Oscillator is intended for calibration to 1.0, 2.0, 4.0, or

8.0 MHz. Tuning to other values is not guaranteed, as indicated in Table 11.

Table 10. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection

SUT1..0

Start-up Time from

Power-down and

Power-save

Additional Delay

from Reset

(VCC = 5.0V)

Recommended Usage

6 CK

–

BOD enabled

6 CK

4.1 ms

Fast rising power

(1)

6 CK

65 ms

Slowly rising power

Reserved

Bit

765

432

CAL7

CAL6

CAL5

CAL4

CAL3

CAL2

CAL1

CAL0

OSCCAL

Read/Write

R/W

Initial Value

Device Specific Calibration Value

Table 11. Internal RC Oscillator Frequency Range.

OSCCAL Value

Min Frequency in Percentage of

Nominal Frequency (%)

Max Frequency in Percentage of

Nominal Frequency (%)

$00

100

$7F

150

$FF

100

200

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