AT90PWM2B-16SE ATMEL [ATMEL Corporation], AT90PWM2B-16SE Datasheet - Page 30

• Manufacturer Part Number: AT90PWM2B-16SE
• Description: 8-bit Microcontroller with 8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

7.1.5
7.2
30
Clock Sources
AT90PWM2/3/2B/3B
ADC Clock – clk
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 7-1. The clock from the selected source is input to the AVR clock generator, and routed to
the appropriate modules.
Table 7-1.
Note:
Table 7-2.
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-
ADC
Device Clocking Option
External Crystal/Ceramic Resonator
Reserved
PLL output divided by 4 : 16 MHz
Calibrated Internal RC Oscillator
Reserved
External Clock
Device Clocking Option
External Crystal/Ceramic Resonator
PLL output divided by 4 : 16 MHz / External
Crystal/Ceramic Resonator/ PLL driven by External Crystal
/Ceramic Resonator
PLL output divided by 4 : 16 MHz / PLL driven by External
Crystal/Ceramic Resonator
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
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
1. For all fuses “1” means unprogrammed while “0” means programmed.
Device Clocking Options Select
Device Clocking Options Select AT90PWM2B/3B
(1)
AT90PWM2/3
System
Clock
Ext Osc
Ext Osc
PLL / 4
N/A
PLL / 4
RC Osc
PLL / 4
Ext Clk
(2)
PLL Input
RC Osc
Ext Osc
Ext Osc
N/A
RC Osc
RC Osc
Ext Clk
RC Osc
(4)
(3)
1111 - 1000
0111- 0100
CKSEL3..0
0011
0010
0001
0000
1111 - 1000
0111- 0110
4317J–AVR–08/10
CKSEL3..0
0100
0101
0011
0010
0001
0000
(1)