MEGA128CAN Datasheet, PDF (39/413 Pages) ATMEL Corporation – Microcontroller WITH 128K BYTES OF ISP FLASH AND CAN CONTROLLER

AT90CAN128
When this Oscillator is selected, start-up times are determined by the SUT Fuses as
shown in Table 12.
Table 12. Start-up times for the internal calibrated RC Oscillator clock selection
SUT1..0
00
Start-up Time from Power-
down and Power-save
6 CK
Additional Delay from
Reset (V_CC = 5.0V)
14CK
Recommended Usage
BOD enabled
01
10⁽¹⁾
6 CK
6 CK
14CK + 4.1 ms
14CK + 65 ms
Fast rising power
Slowly rising power
11
Reserved
Note: 1. The device is shipped with this option selected.
Oscillator Calibration Register
– OSCCAL
Bit
Read/Write
Initial Value
7
6
5
4
3
2
1
0
–
CAL6
CAL5
CAL4
CAL3
CAL2
CAL1
CAL0 OSCCAL
R
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
<----- ------
Device Specific Calibration Value
------ ----->
• 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.
Table 13. Internal RC Oscillator Frequency Range.
Min Frequency in Percentage of
OSCCAL Value
Nominal Frequency
0x00
50%
0x3F
75%
0x7F
100%
Max Frequency in Percentage of
Nominal Frequency
100%
150%
200%
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”.
39
4250E–CAN–12/04