ATMEGA328P-20PU Atmel, ATMEGA328P-20PU Datasheet - Page 35

• Manufacturer Part Number: ATMEGA328P-20PU
• Manufacturer: Atmel

Specifications of ATMEGA328P-20PU

• Cpu Family: ATmega
• Device Core: AVR
• Device Core Size: 8b
• Frequency (max): 20MHz
• Interface Type: SPI/TWI/USART
• Program Memory Type: Flash
• Program Memory Size: 32KB
• Total Internal Ram Size: 2KB
• # I/os (max): 23
• Number Of Timers - General Purpose: 3
• Operating Supply Voltage (typ): 3.3/5V
• Operating Supply Voltage (max): 5.5V
• Operating Supply Voltage (min): 2.7V
• On-chip Adc: 6-chx10-bit
• Instruction Set Architecture: RISC
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Through Hole
• Pin Count: 28
• Package Type: PDIP
• Lead Free Status / Rohs Status: Compliant

8.9
8.10
8.11
8025K–AVR–10/09
Clock Output Buffer
Timer/Counter Oscillator
System Clock Prescaler
When this clock source is selected, start-up times are determined by the SUT Fuses as shown in
Table
Table 8-16.
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. If changes of more than 2% is
required, ensure that the MCU is kept in Reset during the changes.
Note that the System Clock Prescaler can be used to implement run-time changes of the internal
clock frequency while still ensuring stable operation. Refer to
35
The device can output the system clock on the CLKO pin. To enable the output, the CKOUT
Fuse has to be programmed. This mode is suitable when the chip clock is used to drive other cir-
cuits on the system. The clock also will be output during reset, and the normal operation of I/O
pin will be overridden when the fuse is programmed. Any clock source, including the internal RC
Oscillator, can be selected when the clock is output on CLKO. If the System Clock Prescaler is
used, it is the divided system clock that is output.
ATmega48P/88P/168P uses the same crystal oscillator for Low-frequency Oscillator and
Timer/Counter Oscillator. See
oscillator and crystal requirements.
ATmega48P/88P/168P share the Timer/Counter Oscillator Pins (TOSC1 and TOSC2) with
XTAL1 and XTAL2. When using the Timer/Counter Oscillator, the system clock needs to be four
times the oscillator frequency. Due to this and the pin sharing, the Timer/Counter Oscillator can
only be used when the Calibrated Internal RC Oscillator is selected as system clock source.
Applying an external clock source to TOSC1 can be done if EXTCLK in the ASSR Register is
written to logic one. See
description on selecting external clock as input instead of a 32.768 kHz watch crystal.
The ATmega48P/88P/168P has a system clock prescaler, and the system clock can be divided
by setting the
decrease the system clock frequency and the power consumption when the requirement for pro-
cessing power is low. This can be used with all clock source options, and it will affect the clock
BOD enabled
Fast rising power
Slowly rising power
for details.
Power Conditions
8-16.
Start-up Times for the External Clock Selection
”CLKPR – Clock Prescale Register” on page
”Asynchronous Operation of Timer/Counter2” on page 152
Start-up Time from Power-
”Low Frequency Crystal Oscillator” on page 32
down and Power-save
Reserved
6 CK
6 CK
6 CK
ATmega48P/88P/168P
Additional Delay from
”System Clock Prescaler” on page
377. This feature can be used to
Reset (V
14CK + 4.1 ms
14CK + 65 ms
14CK
CC
= 5.0V)
for details on the
for further
SUT1..0
00
01
10
11
35