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CLOCK CIRCUITS
27MHz X'TAL (X1201)
Block diagram for 27 MHz clock circuit is shown in Fig. 5-8-1.
When power is supplied to 27 MHz X'TAL, it generates 27MHz clock and input it to A/V processor (IC1201),
video encoder (IC2201).
1.
A/V PROCESSOR
The A/V processor uses it as CLOCK PCLK2X (input at pins 117) of video interface signal and output
digital video stream synchronized to PCLK2X from 8bit video data bus VDATA[7:0] (output at pins 106,
107, 108, 109, 110, 113, 114, 115 )
2.
VIDEO ENCODER
At video encoder it is used as system clock CLK (input at pin 44) and output horizontal synchronous
HSYNC (output at pin 15 ) and vertical synchronous VSYNC (output at pin 16) to A/V processor.
3.
Audio DA Converter
The audio external frequency clock signal DA-XCK is used as system clock. DA-XCK is supplied from A/V
processor (output at pin 39 ) to Audio DAC (input at IC1501~IC1503 pin 5).
IC1201: The DA-XCK is used to generates Audio bit clock TBCK (output at pin 40) and LR clock TWS
(output at pin 32).
DA-XCK
TBCK
TWS
* The Audio Interface Unit inside A/V processor corresponds to sampling frequencies (fs) 44.1kHz (CD-DA,
Video-CD), 48kHz, 96kHz (DVD).
The frequency of TBCK is defined by Formula 1:
f TBCK = Audio data bit length * 2 * fs .......................................................................................................1
At A/V decoder, interior DA-XCK is divided into 8 equal parts and output as TBCK
(Formula 2)
f TBCK = f DA-XCK /8 ...............................................................................................................................2
Therefore, DA-XCX frequency takes the value 384fs according to formulas 1 and 2. Audio data bit length is
fixed 24bit. (Formula 3)
f DA-XCX = Audio data bit length * 2 * fs * 8 = 24 * 2 * fs * 8=384 fs.........................................................3
According to Formulas 2 and 3, A/V decoder drives TBCK
with frequency 48 times of sampling frequency. (Formula 4)
f TBCK =384fs/8 = 48fs..............................................................................................................................4
The relationships between Audio interface signals (DA-XCK, TWS, TBCK) and each sampling frequency are
as follows:
6
Sampling frequency: 44.1 kHz (For CD-DA and Video-CD)
DA-XCK
TBCK
TWS
6
Sampling frequency: 48kHz (for DVD)
DA-XCK
TBCK
TWS
Chapter 1
Is interior clock used for generating TBCK and TWS, DA-XCK takes frequency 384 times the
sampling frequency.
Is Audio bit clock obtained by dividing DA-XCK in 8 equal parts. It takes frequency 48 times
that of sampling.
Is clock that identifies channel (Lch or Rch) against all Audio sampling.
384*fs=16.934MHz
DA-XCK/8=2.1168MHz
TBCK/48=44.1kHz=fs
384*fs=18.432MHz
DA-XCK/8=2.304MHz
TBCK/48=48kHz=fs
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