ATMEGA325A-AUR Atmel, ATMEGA325A-AUR Datasheet - Page 31

• Manufacturer Part Number: ATMEGA325A-AUR
• Description: IC MCU AVR 32K FLASH 64TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA325A-AUR

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: SPI, UART/USART, USI
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 54
• Program Memory Size: 32KB (16K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 1K x 8
• Ram Size: 2K 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: 64-TQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

8.3
8.4
8285B–AVR–03/11
Default Clock Source
Calibrated Internal RC Oscillator
ATmega165A/165PA/325A/325PA/3250A/3250PA/6
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The default
clock source setting is the Internal RC Oscillator with longest start-up time and an initial system
clock prescaling of 8. This default setting ensures that all users can make their desired clock
source setting using an In-System or Parallel programmer.
By default, the Internal RC Oscillator provides an approximate 8MHz clock. Though voltage and
temperature dependent, this clock can be very accurately calibrated by the user. See
11 on page 325
shipped with the CKDIV8 Fuse programmed. See
more details.
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 cali-
brates the RC Oscillator. The accuracy of this calibration is shown as Factory calibration in
27-11 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 8-3.
Notes:
When this Oscillator is selected, start-up times are determined by the SUT Fuses as shown in
Table 8-4
Table 8-4.
Note:
Power Conditions
BOD enabled
Fast rising power
Slowly rising power
37, it is possible to get a higher calibration accuracy than by using the factory calibration.
8-3. If selected, it will operate with no external components. During reset, hardware loads
1. The device is shipped with this option selected.
2. The frequency ranges are preliminary values.
3. If 8MHz frequency exceeds the specification of the device (depends on V
1. 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
325.
Frequency Range
and
”Internal Oscillator Speed” on page 356
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
”System Clock Prescaler” on page 36
.
286.
Additional Delay from
Reset (V
Table 27-11 on page
for more details. The device is
14CK + 65ms
14CK + 4.1ms
(1)(3)
14CK
CC
CKSEL3:0
= 5.0V)
0010
(1)
CC
), the CKDIV8
325.
Table 27-
SUT1:0
00
01
10
11
Table
for
31