ATMEGA48V_11 ATMEL [ATMEL Corporation], ATMEGA48V_11 Datasheet - Page 28

• Manufacturer Part Number: ATMEGA48V_11
• Description: 8-bit Atmel Microcontroller with 4/8/16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

9.1.4
9.1.5
9.2
9.2.1
9.2.2
2545T–AVR–05/11
Clock sources
Asynchronous timer clock – clk
ADC clock – clk
Default clock source
Clock startup sequence
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.
Note:
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
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
Oscillator and the number of cycles in the delay is set by the SUTx and CKSELx fuse bits. The
ADC
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
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
CC
to start oscillating and a minimum number of oscillating
(1)
.
“System control and reset” on page 45
ATmega48/88/168
TOUT
1111 - 1000
0111 - 0110
0101 - 0100
CKSEL3..0
) is timed from the Watchdog
0011
0010
0000
0001
TOUT
) after
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