ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 26

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ATmega88PA Automotive

Manufacturer Part Number
ATmega88PA Automotive
Description
Manufacturer
Atmel Corporation
7.1.4
7.2
7.3
26
Clock Sources
Default Clock Source
Atmel ATtiny24/44/84 [Preliminary]
ADC Clock – clk
ADC
The ADC is provided with a dedicated clock domain. This allows halting the CPU and I/O
clocks in order to reduce noise generated by their digital circuitry. This gives more accurate
ADC conversion results.
The device has the following clock source options, selectable by Flash Fuse bits as shown
below. The clock from the selected source is input to the Atmel
routed to the appropriate modules.
Table 7-1.
Note:
The various choices for each clocking option is given in the following sections. When the CPU
wakes up from power-down or power-save, the selected clock source is used to time the
start-up, ensuring stable oscillator operation before instruction execution starts. When the
CPU starts from reset, there is an additional delay allowing the power to reach a stable level
before commencing normal operation. The watchdog oscillator is used for timing this real-time
part of the start-up time. The number of WDT oscillator cycles used for each time-out is shown
in
Table 7-2.
The device is shipped with CKSEL = “0010”, SUT = “10”, and CKDIV8 programmed. The
default clock source setting is therefore the Internal RC Oscillator running at 8.0MHz with lon-
gest start-up time and an initial system clock prescaling of 8, resulting in 1.0MHz system clock.
This default setting ensures that all users can make their desired clock source setting using an
In-System or High-voltage Programmer.
Device Clocking Option
External Clock
Calibrated Internal RC Oscillator 8.0MHz
Watchdog Oscillator 128kHz
External Low-frequency Oscillator
External Crystal/Ceramic Resonator
Reserved
Table 7-2 on page
1. For all fuses “1” means unprogrammed while “0” means programmed.
Typ Time-out
Device Clocking Options Select
Number of Watchdog Oscillator Cycles
64ms
4ms
26.
(1)
Number of Cycles
8K (8,192)
®
512
AVR
0101, 0111, 0011,0001
®
clock generator, and
CKSEL3..0
1000-1111
0000
0010
0100
0110
7701E–AVR–02/11

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