AT90PWM81 View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'AT90PWM81' PDF : 325 Pages View PDF
AT90PWM81/161
5.1.2
Data memory holding the Stack Pointer. Halting the CPU clock inhibits the core from performing
general operations and calculations.
clkI/O - I/O Clock
The I/O clock is used by the majority of the I/O modules, like Timer/Counter. The I/O clock is
also used by the External Interrupt module, but note that some external interrupts are detected
by asynchronous logic, allowing such interrupts to be detected even if the I/O clock is halted.
5.1.3
clkFLASH - Flash Clock
The Flash clock controls operation of the Flash interface. The Flash clock is usually active simul-
taneously with the CPU clock.
5.1.4
clkPLL - PLL Clock
The PLL clock allows the PSC modules to be clocked directly from a 64/32MHz clock. A 16MHz
clock is also derived for the CPU.
5.1.5
clkADC - ADC 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.
5.2 Clock Sources
The device has the following clock source options, selectable by Flash Fuse bits (default) or by
the CLKSELR register (dynamic clock switch circuit) as shown below. The clock from the
selected source is input to the AVR clock generator, and routed to the appropriate modules.
Table 5-1. Device clocking options select (1) , PLL source and PE1 and PE2 functionality.
Device clocking option
System
clock
CKSEL3..0 (3)
PLL input (2) CSEL3..0 (4)
External clock
Ext Clk (8)
RC Osc (6)
0000
PLL output divided by 4 : 16MHz driven by internal RC PLL / 4
RC Osc (6)
0001
Calibrated internal RC oscillator 8MHz
RC Osc (6) RC Osc (6)
0010
Internal 128kHz RC oscillator (WD)
WD (7)
N/A
0011
PLL output divided by 4 / PLL driven by external
crystal/ceramic resonator
PLL / 4
Ext Osc (5)
0100
PLL output divided by 4/ PLL driven by external clock PLL / 4
Ext Clk (8)
0101
Calibrated internal RC oscillator 1MHz
RC Osc (6) N/A
0110
External crystal/ceramic resonator (3.0MHz - 8.0MHz)
External crystal/ceramic resonator (0.9MHz - 3.0MHz)
External crystal/ceramic resonator (0.9MHz - 3.0MHz)
External crystal/ceramic resonator (3.0MHz - 8.0MHz)
External crystal/ceramic resonator (3.0MHz - 8.0MHz)
External crystal/ceramic resonator (3.0MHz - 8.0MHz)
Ext Osc (5)
Ext Osc (5)
Ext Osc (5)
Ext Osc (5)
Ext Osc (5)
Ext Osc (5)
Ext Osc (5)
RC Osc (6)
RC Osc (6)
RC Osc (6)
RC Osc (6)
RC Osc (6)
0111 b
1000 b
1001 b
1010 b
1011 b
1100 b
PE1
CLKI
I/O
I/O
I/O
XTAL1
CLKI
I/O
XTAL1
XTAL1
XTAL1
XTAL1
XTAL1
XTAL1
PE2
I/O
I/O
I/O
I/O
XTAL2
I/O
I/O
XTAL2
XTAL2
XTAL2
XTAL2
XTAL2
XTAL2
28
7734Q–AVR–02/12
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