ATMEGA644A-PU Atmel, ATMEGA644A-PU Datasheet - Page 37

• Manufacturer Part Number: ATMEGA644A-PU
• Description: IC MCU AVR 64K FLASH 40PDIP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA644A-PU

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 32
• Program Memory Size: 64KB (32K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 2K x 8
• Ram Size: 4K x 8
• Voltage - Supply (vcc/vdd): 1.8 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 40-DIP (0.600", 15.24mm)
• Processor Series: ATmega
• Core: AVR
• Data Bus Width: 8 bit
• Data Ram Size: 4 KB
• Interface Type: JTAG, TWI, SPI, USART
• Maximum Clock Frequency: 20 MHz
• Number Of Programmable I/os: 32
• Number Of Timers: 3
• Operating Supply Voltage: 3.3 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: Through Hole
• Minimum Operating Temperature: - 40 C
• Operating Temperature Range: - 40 C to + 85 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

8.6
8272A–AVR–01/10
Calibrated Internal RC Oscillator
By default, the Internal RC Oscillator provides an approximate 8 MHz clock. Though voltage and
temperature dependent, this clock can be very accurately calibrated by the the user. See
27-10 on page 334
The device is shipped with the CKDIV8 Fuse programmed. See
page 40
This clock may be selected as the system clock by programming the CKSEL Fuses as shown in
Table
the pre-programmed calibration value into the OSCCAL Register and thereby automatically cal-
ibrates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in
Table 27-10 on page
By changing the OSCCAL register from SW, see
page
The accuracy of this calibration is shown as User calibration in
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 8-10.
Notes:
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 8-11 on page
Table 8-11.
Note:
164A/164PA/324A/324PA/644A/644PA/1284/1284P
Power Conditions
BOD enabled
Fast rising power
Slowly rising power
41, it is possible to get a higher calibration accuracy than by using the factory calibration.
8-10. If selected, it will operate with no external components. During reset, hardware loads
1. The device is shipped with this option selected.
2. If 8 MHz frequency exceeds the specification of the device (depends on V
1.
for more details.
The device is shipped with this option selected.
Fuse can be programmed in order to divide the internal frequency by 8.
Internal Calibrated RC Oscillator Operating Modes
Start-up times for the Internal Calibrated RC Oscillator clock selection
Frequency Range
and
37.
334.
”Internal Oscillator Speed” on page 387
7.3 - 8.1
Start-up Time from Power-
”Calibration Byte” on page
down and Power-save
(2)
(MHz)
Reserved
6 CK
6 CK
6 CK
”OSCCAL – Oscillator Calibration Register” on
298.
Additional Delay from
Reset (V
Table 27-10 on page
14CK + 4.1 ms
and
14CK + 65 ms
”System Clock Prescaler” on
14CK
page 439
CC
CKSEL3..0
= 5.0V)
0010
CC
(1)
for more details.
), the CKDIV8
334.
SUT1..0
10
00
01
11
Table
(1)
37