CS4923 datasheet(32/56 Pages) CIRRUS

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CS4923/4/5/6/7/8/9

DS262F2

CLOCKING

Revision D

of the CS4923/4/5/6/7/8/9 also

incorporates a programmable phase locked loop

(PLL) clock synthesizer. The PLL takes an input

reference clock and produces all the internal clocks

required to run the internal DSP and to provide

master mode timing to the audio input/output

peripherals. The clock manager also includes a

33-bit system time clock (STC) to support audio

and

video

synchronization

broadcast

applications.

The PLL can be internally bypassed by connecting

the CLKSEL

to VD.

This connection

multiplexes the CLKIN pin directly to the DSP

clock. Care should be taken to note the minimum

CLKIN requirements when bypassing the PLL.

The PLL reference clock has three possible sources

that are routed through a multiplexer controlled by

the DSP: SCLKN2, SCLKN1, and CLKIN.

Typically, in audio/video environments like set-top

boxes, the CLKIN pin is connected to 27 MHz. In

other scenarios such as an A/V receiver design, the

PLL can be clocked through the CLKIN pin with

even multiples of the desired sampling rate or with

an already available clock source. CLKIN is

typically a multiple of a standard sampling

frequency in this scenario (e.g. 11.2896 MHz).

The clock manager is controlled by the DSP

application software. Please refer to the Hardware

User’s Guide for the CS4923/4/5/6/7/8/9 (AN115)

and all relevant application code user’s guides for

information on supported CLKIN frequencies and

how to set up and control the internal PLL.

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