atmega32c1 ATMEL Corporation, atmega32c1 Datasheet - Page 33

• Manufacturer Part Number: atmega32c1
• Description: Atmega32m1 Automotive 8-bit Avr Microcontroller With 32k/64k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

5.5.1
7647A–AVR–02/08
Oscillator Calibration Register – OSCCAL
ibrates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in
Table 25-1 on page
By changing the OSCCAL register from SW, see
page
The accuracy of this calibration is shown as User calibration in
312.
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 more information on the pre-programmed cali-
bration value, see the section .
Table 5-5.
Notes:
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 5-6 on page
Table 5-6.
Note:
• Bits 7..0 – CAL7..0: Oscillator Calibration Value
The Oscillator Calibration Register is used to trim the Calibrated Internal RC Oscillator to
remove process variations from the oscillator frequency. The factory-calibrated value is automat-
ically written to this register during chip reset, giving an oscillator frequency of 8.0 MHz at 25°C.
The application software can write this register to change the oscillator frequency. The oscillator
can be calibrated to any frequency in the range 7.3 - 8.1 MHz within ±1% accuracy. Calibration
outside that range is not guaranteed.
Note that this oscillator is used to time EEPROM and Flash write accesses, and these write
times will be affected accordingly. If the EEPROM or Flash are written, do not calibrate to more
than 8.8 MHz. Otherwise, the EEPROM or Flash write may fail.
Bit
Read/Write
Initial Value
Power Conditions
BOD enabled
Fast rising power
Slowly rising power
33, it is possible to get a higher calibration accuracy than by using the factory calibration.
1. The device is shipped with this option selected.
2. If 8 MHz frequency exceeds the specification of the device (depends on V
1. If the RSTDISBL fuse is programmed, this start-up time will be increased to
2.
Fuse can be programmed in order to divide the internal frequency by 8.
14CK + 4.1 ms to ensure programming mode can be entered.
The device is shipped with this option selected.
Frequency Range (MHz)
Internal Calibrated RC Oscillator Operating Modes
Start-up times for the internal calibrated RC Oscillator clock selection
CAL7
R/W
7
33.
312.
7.3 - 8.1
CAL6
R/W
6
Start-up Time from Power-
down and Power-save
CAL5
R/W
5
Device Specific Calibration Value
Reserved
6 CK
6 CK
6 CK
CAL4
R/W
4
“Oscillator Calibration Register – OSCCAL” on
CAL3
R/W
3
ATmega32/64/M1/C1
CAL2
Additional Delay from
R/W
2
Reset (V
“Clock Characteristics” on page
14CK + 65 ms
14CK + 4.1 ms
(1)(2)
CKSEL3..0
14CK
0010
CAL1
R/W
CC
1
(1)
= 5.0V)
(2)
CC
CAL0
R/W
), the CKDIV8
0
SUT1..0
OSCCAL
00
01
10
11
33