atmega32c1 ATMEL Corporation, atmega32c1 Datasheet - Page 30

• Manufacturer Part Number: atmega32c1
• Description: Atmega32m1 Automotive 8-bit Avr Microcontroller With 32k/64k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

5.1.4
5.1.5
5.2
30
Clock Sources
ATmega32/64/M1/C1
PLL Clock – clk
ADC Clock – clk
The PLL clock allows the fast peripherals to be clocked directly from a 64/32 MHz clock. A 16
MHz clock is also derived for the CPU.
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 illustrated
Table 5-1. The clock from the selected source is input to the AVR clock generator, and routed to
the appropriate modules.
Table 5-1.
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 starting
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
PLL
Device Clocking Option
External Crystal/Ceramic Resonator
PLL output divided by 4 : 16 MHz / PLL driven by External
Crystal/Ceramic Resonator
PLL output divided by 4 : 16 MHz / PLL driven by External
Crystal/Ceramic Resonator
Reserved
Reserved
PLL output divided by 4 : 16 MHz
Calibrated Internal RC Oscillator
PLL output divided by 4 : 16 MHz / PLL driven by External
clock
External Clock
ADC
1. For all fuses “1” means unprogrammed while “0” means programmed.
2. Ext Osc : External Osc
3. RC Osc : Internal RC Oscillator
4. Ext Clk : External Clock Input
Device Clocking Options Select
(1)
System
Clock
Ext Osc
Ext Osc
PLL / 4
N/A
N/A
PLL / 4
RC Osc
PLL / 4
Ext Clk
PLL Input
RC Osc
Ext Osc
Ext Osc
N/A
N/A
RC Osc
RC Osc
Ext Clk
RC Osc
Table
7647A–AVR–02/08
1111 - 1000
CKSEL3..0
0100
0101
0010
0001
0000
0110
0111
0011
5-2. The