ATMEga64L ATMEL Corporation, ATMEga64L Datasheet - Page 40

• Manufacturer Part Number: ATMEga64L
• Description: 8-bit AVR Microcontroller with 64K Bytes In-System Programmable Flash
• Manufacturer: ATMEL Corporation

Calibrated Internal RC
Oscillator
Oscillator Calibration Register
– OSCCAL
40
ATmega64(L)
(1)
The calibrated internal RC Oscillator provides a fixed 1.0, 2.0, 4.0, or 8.0 MHz clock. All
frequencies are nominal values at 5V and 25°C. This clock may be selected as the sys-
tem clock by programming the CKSEL Fuses as shown in Table 13. If selected, it will
operate with no external components. The CKOPT Fuse should always be unpro-
grammed when using this clock option. During reset, hardware loads the calibration byte
into the OSCCAL Register and thereby automatically calibrates the RC Oscillator. At 5V,
25°C and 1.0 MHz Oscillator frequency selected, this calibration gives a frequency
within ± 3% of the nominal frequency. Using run-time calibration methods as described
in application notes available at www.atmel.com/avr it is possible to achieve ± 1% accu-
racy at any given V
the Watchdog Oscillator will still be used for the Watchdog Timer and for the Reset
Time-out. For more information on the preprogrammed calibration value, see the section
“Calibration Byte” on page 293.
Table 13. Internal Calibrated RC Oscillator Operating Modes
Note:
When this Oscillator is selected, start-up times are determined by the SUT Fuses as
shown in Table 14. XTAL1 and XTAL2 should be left unconnected (NC).
Table 14. Start-up Times for the Internal Calibrated RC Oscillator Clock Selection
Note:
Note:
• 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. During Reset, the 1 MHz calibration value
which is located in the signature row high byte (address 0x00) is automatically loaded
into the OSCCAL Register. If the internal RC is used at other frequencies, the calibration
values must be loaded manually. This can be done by first reading the signature row by
a programmer, and then store the calibration values in the Flash or EEPROM. Then the
Bit
Read/Write
Initial Value
SUT1..0
10
00
01
11
(1)
1. The device is shipped with this option selected.
1. The device is shipped with this option selected.
1. The OSCCAL Register is not available in ATmega103 compatibility mode.
CKSEL3..0
Start-up Time from Power-
0001
CAL7
down and Power-save
0010
0011
0100
R/W
7
(1)
CC
and Temperature. When this Oscillator is used as the chip clock,
CAL6
6 CK
6 CK
6 CK
R/W
6
CAL5
R/W
5
Device Specific Calibration Value
CAL4
R/W
4
Additional Delay from
Reset (V
Reserved
CAL3
R/W
Nominal Frequency (MHz)
4.1 ms
3
65 ms
CC
–
= 5.0V)
CAL2
R/W
2
1.0
2.0
4.0
8.0
CAL1
R/W
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
1
CAL0
R/W
0
2490G–AVR–03/04
OSCCAL