U s i n g t h e e x t e r n a l o s c i l l a t o r
5 0
N S 7 5 2 0 H a r d w a r e R e f e r e n c e , R e v G 9 / 2 0 0 7
NS7520 clock module block diagram
This diagram provides an overview of the clock module.
Using the external oscillator
The NS7520 can use an external oscillator to generate the BCLK and FXTAL signals. In
this type of configuration, the BCLK frequency is equal to the oscillator input
frequency. The FXTAL frequency is equal to the oscillator input frequency divided by
five. For example, with a 55MHz oscillator, BCLK would be 55 MHZ and FXTAL would
be 11MHz.
Note:
Using an external oscillator with PLL enabled is not advantageous, due to
the PLL input limitation of 10MHz to 20MHz. The oscillator needs to be the
same frequency as the crystal. Using a clock source greater than 20MHz
would result in the PLL running outside its operating range.
External oscillator mode hardware configuration
The external oscillator’s output is connected to the XTALA1 input through a 100
resistor. XTALA2 is an output and is left open.
PLL
circuit
SCANEN
PLLTST
BISTEN
External
crystal
External
oscillator
A[8:0]
PLL Settings reg
PLL Control reg
/5
FXTAL
BCLK
Summary of Contents for NS7520B Series
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