ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 27

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

9.1.3
9.1.4
9.1.5
9.2
9.2.1
9.2.2
9223B–AVR–09/11
Clock Sources
Flash Clock – clk
Asynchronous Timer Clock – clk
ADC Clock – clk
Default Clock Source
Clock Startup Sequence
ADC
The Flash clock controls operation of the Flash interface. The Flash clock is usually active
simultaneously with the CPU clock.
The Asynchronous Timer clock allows the Asynchronous Timer/Counter to be clocked directly
from an external clock or an external 32kHz clock crystal. The dedicated clock domain allows
using this Timer/Counter as a real-time counter even when the device is in sleep mode.
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 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 AVR clock generator, and routed to
the appropriate modules.
Table 9-1.
The device is shipped with internal RC oscillator at 8.0MHz and with the fuse CKDIV8 pro-
grammed, resulting in 1.0MHz system clock. The startup time is set to maximum and time-out
period enabled. (CKSEL = "0010", SUT = "10", CKDIV8 = "0"). The default setting ensures
that all users can make their desired clock source setting using any available programming
interface.
Any clock source needs a sufficient V
ing cycles before it can be considered stable.
To ensure sufficient V
the device reset is released by all other reset sources.
describes the start conditions for the internal reset. The delay (t
dog Oscillator and the number of cycles in the delay is set by the SUTx and CKSELx fuse bits.
The selectable delays are shown in
voltage dependent as shown in
FLASH
Device Clocking Option
Low Power Crystal Oscillator
Full Swing Crystal Oscillator
Low Frequency Crystal Oscillator
Internal 128kHz RC Oscillator
Calibrated Internal RC Oscillator
External Clock
Reserved
Note:
Atmel ATmega48PA/88PA/168PA [Preliminary]
1. For all fuses “1” means unprogrammed while “0” means programmed.
Device Clocking Options Select
ASY
CC
, the device issues an internal reset with a time-out delay (t
“Typical Characteristics” on page
Table
CC
to start oscillating and a minimum number of oscillat-
9-2. The frequency of the Watchdog Oscillator is
(1)
“System Control and Reset” on page 47
TOUT
1111 - 1000
0111 - 0110
0101 - 0100
CKSEL3...0
325.
) is timed from the Watch-
0011
0010
0000
0001
TOUT
) after
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