MEGA128CAN datasheet(39/413 Pages) ATMEL

39 / 413 page

AT90CAN128

4250E–CAN–12/04

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

shown in Table 12.

Note:

1. The device is shipped with this option selected.

Oscillator Calibration Register

– OSCCAL

• Bit 7 – Reserved Bit

This bit is reserved for future use.

• Bits 6..0 – CAL6..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

0x7F 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 8.0 MHz. Tuning to

other values is not guaranteed, as indicated in Table 13.

External Clock

To drive the device from an external clock source, XTAL1 should be driven as shown in

Figure 22. To run the device on an external clock, the CKSEL Fuses must be pro-

grammed to “0000”.

Table 12. 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 (V

CC = 5.0V)

Recommended Usage

6 CK

14CK

BOD enabled

6 CK

14CK + 4.1 ms

Fast rising power

(1)

6 CK

14CK + 65 ms

Slowly rising power

Reserved

Bit

765

432

–

CAL6

CAL5

CAL4

CAL3

CAL2

CAL1

CAL0

OSCCAL

Read/Write

R/W

Initial Value

<----- ------

Device Specific Calibration Value

------ ----->

Table 13. Internal RC Oscillator Frequency Range.

OSCCAL Value

Min Frequency in Percentage of

Nominal Frequency

Max Frequency in Percentage of

Nominal Frequency

0x00

50%

100%

0x3F

75%

150%

0x7F

100%

200%

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