Datasheet

2503Q–AVR–02/11

ATmega32(L)

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

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

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

ations from the Oscillator frequency. During Reset, the 1MHz calibration value which is located

in the signature row High Byte (address 0x00) is automatically loaded into the OSCCAL Regis-

ter. 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 value can be read by software and

loaded into the OSCCAL Register. When OSCCAL is zero, the lowest available frequency is

chosen. Writing non-zero values to this register will increase the frequency of the Internal Oscil-

lator. 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 calibrate 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, 2.0z, 4.0, or 8.0MHz. 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

= 5.0V) Recommended Usage

00 6 CK – BOD enabled

01 6 CK 4.1ms Fast rising power

(1)

6 CK 65ms Slowly rising power

11 Reserved

Bit 76543210

CAL7 CAL6 CAL5 CAL4 CAL3 CAL2 CAL1 CAL0 OSCCAL

Read/Write R/W R/W R/W R/W R/W R/W R/W 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 50 100

$7F 75 150

$FF 100 200