ADV8003 Hardware Manual
Rev. B, August 2013
273
DIVIDE
BY
N
DIVIDE
BY
CTS
CTS
1
N
1
TMDS
CLOCK
VIDEO CLOCK
N
128 ×
f
S
128 ×
f
S
SINK DEVICE
SOURCE DEVICE
1
N AND CTS VALUES ARE TRANSMITTED USING THE “AUDIO CLOCK REGENERATION”
PACKET. VIDEO CLOCK IS TRANSMITTED ON TMDS CLOCK CHANNEL.
REGISTER
N
MULTIPLY
BY
N
CYCLE
TIME
COUNTER
06076-
008
Figure 96: Audio Clock Regeneration
illustrates the overall system architecture model used by HDMI Rxs for audio clock regeneration. The HDMI source determines
the fractional relationship between the video clock and an audio reference clock (128*fs) and passes the numerator and denominator for
that fraction to the sink across the HDMI link. The sink may then recreate the audio clock from the TMDS clock by using a clock divider
and a clock multiplier. The relationship between the two clocks is shown in
CTS
N
f
f
CLK
TMDS
s
_
128
=
Equation 20: Relationship Between Audio Reference and TMDS Clocks
The source determines the value of the numerator N as specified in the HDMI specification. Typically, this value N is used in a clock
divider to generate an intermediate clock that is slower than the 128*fs clock by the factor N. The source typically determines the value of
the denominator Cycle Time Stamp (CTS) by counting the number of TMDS clocks in each of the 128*fs/N clocks.
6.11.3.1.
N Parameter
N is an integer number and is calculated using
with the recommended optimal value shown in
which
approximately equals N for coherent audio and video clock sources.
can be used to determine the value of N. For non
coherent sources or sources where coherency is not known,
and
should be used.
128*fS/1500Hz ≤N ≤128*fS/300Hz
Equation 21: Restriction for N Value
128*fs/1000Hz
Equation 22: Optimal N Value
6.11.3.2.
CTS Parameter
The CTS value is an integer number that satisfies
s
CLK
TMDS
Average
f
N
f
CTS
128
_
=
Equation 23: Relationship Between N and CTS
6.11.3.3.
Recommended N and Expected CTS Values
The recommended values of N for several standard pixel clocks are given in
The ADV8003 has two modes for CTS generation.
Summary of Contents for ADV8003
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