Atmel ATmega32M1 User Manual

30
7647H–AVR–03/12
Atmel ATmega16/32/64/M1/C1
5.1.3 Flash Clock – clk
FLASH
The Flash clock controls operation of the Flash interface. The Flash clock is usually active simul-
taneously with the CPU clock.
5.1.4 PLL Clock – clk
PLL
The PLL clock allows the fast peripherals to be clocked directly from a 64/32MHz clock. A
16MHz clock is also derived for the CPU.
5.1.5 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 digital circuitry. This gives more accurate ADC conversion
results.
5.2 Clock Sources
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.
Note: 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
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 Table
5-2. The frequency of the Watchdog Oscillator is voltage dependent as shown in “Watchdog
Oscillator Frequency versus V
CC
” on page 342.
Table 5-1. Device Clocking Options Select
(1)
Device Clocking Option
System
Clock PLL Input CKSEL3..0
External Crystal/Ceramic Resonator Ext Osc RC Osc 1111 - 1000
PLL output divided by 4 : 16MHz / PLL driven by External
Crystal/Ceramic Resonator
Ext Osc Ext Osc 0100
PLL output divided by 4 : 16MHz / PLL driven by External
Crystal/Ceramic Resonator
PLL / 4 Ext Osc 0101
Reserved N/A N/A 0110
Reserved N/A N/A 0111
PLL output divided by 4 : 16MHz PLL / 4 RC Osc 0011
Calibrated Internal RC Oscillator RC Osc RC Osc 0010
PLL output divided by 4 : 16MHz / PLL driven by External
clock
PLL / 4 Ext Clk 0001
External Clock Ext Clk RC Osc 0000

Atmel ATmega32M1 Specifications

General

Brand	Atmel
Model	ATmega32M1
Category	Microcontrollers
Language	English