ATA5771 ATMEL Corporation, ATA5771 Datasheet - Page 76

• Manufacturer Part Number: ATA5771
• Manufacturer: ATMEL Corporation

6.1.3
6.1.4
6.2
6.2.1
24
Clock Sources
ATtiny24/44/84
Flash Clock – clk
ADC Clock – clk
External Clock
The Flash clock controls operation of the Flash interface. The Flash clock is usually active simul-
taneously with the CPU clock.
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 6-1.
Note:
The various choices for each clocking option is given in the following sections. When the CPU
wakes up from Power-down the selected clock source is used to time the start-up, ensuring sta-
ble 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 nor-
mal 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 6-2.
To drive the device from an external clock source, CLKI should be driven as shown in
on page
“0000”.
ADC
Device Clocking Option
External Clock (see
Reserved
Calibrated Internal 8 MHz Oscillator (see
Reserved
Internal 128 kHz Oscillator (see
Reserved
Low-Frequency Crystal Oscillator (see
Reserved
Crystal Oscillator / Ceramic Resonator (see
FLASH
1. For all fuses “1” means unprogrammed while “0” means programmed.
25. To run the device on an external clock, the CKSEL Fuses must be programmed to
Typ Time-out
Device Clocking Options Select
Number of Watchdog Oscillator Cycles
64 ms
4 ms
page
24)
page
26)
page
page
page
27)
25)
27)
Number of Cycles
8K (8,192)
512
Table
CKSEL3:0
1000-1111
6-2.
0000
0001
0010
0011
0100
0101
0110
0111
8006G–AVR–01/08
Figure 6-2
(1)