ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 35

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

9.9
9.10
9223B–AVR–09/11
Clock Output Buffer
Timer/Counter Oscillator
When this clock source is selected, start-up times are determined by the SUT Fuses as shown
in
Table 9-16.
When applying an external clock, it is required to avoid sudden changes in the applied clock
frequency 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 inter-
nal clock frequency while still ensuring stable operation. Refer to
page 36
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
circuits 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 inter-
nal 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.
The Atmel
Oscillator and Timer/Counter Oscillator. See
for details on the oscillator and crystal requirements.
Atmel ATmega48PA/88PA/168PA 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 32.768kHz watch crystal.
BOD enabled
Fast rising power
Slowly rising power
Table
Power Conditions
Atmel ATmega48PA/88PA/168PA [Preliminary]
9-16.
for details.
®
ATmega48PA/88PA/168PA uses the same crystal oscillator for Low-frequency
Start-up Times for the External Clock Selection
“Asynchronous Operation of Timer/Counter2” on page 155
Power-down and Power-save
Start-up Time from
Reserved
6 CK
6 CK
6 CK
“Low Frequency Crystal Oscillator” on page 31
Additional Delay from
Reset (V
14CK + 4.1ms
14CK + 65ms
“System Clock Prescaler” on
14CK
CC
= 5.0V)
for further
SUT1...0
10
00
01
11
35