ATMEGA128A-ANR Atmel, ATMEGA128A-ANR Datasheet - Page 44

• Manufacturer Part Number: ATMEGA128A-ANR
• Description: IC MCU AVR 128K FLASH 64TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA128A-ANR

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 16MHz
• Connectivity: EBI/EMI, I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 53
• Program Memory Size: 128KB (64K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 4K x 8
• Ram Size: 4K x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 64-TQFP
• Core: AVR8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

8.9
8.10
8.10.1
8151H–AVR–02/11
Timer/Counter Oscillator
Register Description
OSCCAL - Oscillator Calibration Register
When this clock source is selected, start-up times are determined by the SUT fuses as shown in
Table
Table 8-10.
When applying an external clock, it is required to avoid sudden changes in the applied clock fre-
quency to ensure stable operation of the MCU. A variation in frequency of more than 2% from
one clock cycle to the next can lead to unpredictable behavior. It is required to ensure that the
MCU is kept in Reset during such changes in the clock frequency.
For AVR microcontrollers with Timer/Counter Oscillator pins (TOSC1 and TOSC2), the crystal is
connected directly between the pins. No external capacitors are needed. The Oscillator is opti-
mized for use with a 32.768kHz watch crystal. Applying an external clock source to TOSC1 is
not recommended.
Note:
Note:
• 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 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 calibra-
tion 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 Oscillator. 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
Bit
Read/Write
Initial Value
SUT1:0
00
01
10
11
8-10.
The Timer/Counter Oscillator uses the same type of crystal oscillator as Low-Frequency Oscillator
and the internal capacitors have the same nominal value of 36pF.
OSCCAL Register is not available in ATmega103 compatibility mode.
Start-up Time from Power-
Start-up Times for the External Clock Selection
CAL7
down and Power-save
R/W
7
6CK
6CK
6CK
CAL6
R/W
6
CAL5
R/W
5
Device Specific Calibration Value
CAL4
R/W
4
Additional Delay from
Reset (V
Reserved
CAL3
R/W
4.1ms
65ms
3
CC
–
= 5.0V)
CAL2
R/W
2
CAL1
ATmega128A
R/W
Recommended Usage
BOD enabled
Fast rising power
Slowly rising power
1
CAL0
R/W
0
OSCCAL
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