SAA7118 Datasheet, PDF (67/169 Pages) NXP Semiconductors – Multistandard video decoder with adaptive comb filter and component video input

Philips Semiconductors
Multistandard video decoder with adaptive
comb filter and component video input
Preliminary specification
SAA7118
8.7 Audio clock generation
(subaddresses 30H to 3FH)
The SAA7118 incorporates the generation of a field-locked
audio clock as an auxiliary function for video capture. An
audio sample clock, that is locked to the field frequency,
ensures that there is always the same predefined number
of audio samples associated with a field, or a set of fields.
That ensures synchronous playback of audio and video
after digital recording (e.g. capture to hard disk), MPEG or
other compression, or non-linear editing.
Remark: For standard applications the synthesized audio
clock AMCLK can be used directly as master clock and as
input clock for port AMXCLK (short cut) to generate
ASCLK and ALRCLK. For high-end applications it is
recommended to use an external analog PLL circuit to
enhance the performance of the generated audio clock.
8.7.1 MASTER AUDIO CLOCK
The audio clock is synthesized from the same crystal
frequency as the line-locked video clock is generated. The
master audio clock is defined by the parameters:
• Audio master Clocks Per Field, ACPF[17:0] 32H[1:0]
31H[7:0] 30H[7:0] according to the equation:
ACPF[17:0] = round_^{a--f--ui-e--d--l-d-i-o---f--rf--re--e-q--q-u--u--e--e-n--n-c--c--y-y--}_
• Audio master Clocks Nominal Increment, ACNI[21:0]
36H[5:0] 35H[7:0] 34H[7:0] according to the equation:
ACNI[21:0]
=
round


c--a--r-u-y---sd---ti-ao----l-f--fr-r-e-e--q--q--u-u--e-e--n--n--c-c--y-y-
×
2²³_
See Table 22 for examples.
Table 22 Programming examples for audio master clock generation
XTALO
(MHz)
FIELD
(Hz)
ACPF
DECIMAL
HEX
AMCLK = 256 × 48 kHz (12.288 MHz)
32.11
50
59.94
245 760
205 005
50
−
24.576
59.94
−
AMCLK = 256 × 44.1 kHz (11.2896 MHz)
32.11
50
59.94
225 792
188 348
24.576
50
59.94
225 792
188 348
AMCLK = 256 × 32 kHz (8.192 MHz)
32.11
50
59.94
163 840
136 670
24.576
50
59.94
163 840
136 670
3C000
320CD
−
−
37200
2DFBC
37200
2DFBC
28000
215DE
28000
215DE
ACNI
DECIMAL
HEX
3 210 190
3 210 190
−
−
30FBCE
30FBCE
−
−
2 949 362
2 949 362
3 853 517
3853 517
2D00F2
2D00F2
3ACCCD
3ACCCD
2 140127
2 140 127
2 796 203
2 796 203
20A7DF
20A7DF
2AAAAB
2AAAAB
2001 May 30
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