CS4205_05 Datasheet, PDF (57/81 Pages) Cirrus Logic – CrystalClear® Audio Codec ’97 for Portable Computing

CS4205
7. ZV PORT
The CS4205 implements an asynchronous serial
data input port that conforms to the Zoomed Video
Port (ZV Port) specification. ZV Port data is asyn-
chronous I²S data in PCM format with 16 bits of
resolution. The ZV Port interface consists of four
signals: MCLK, SCLK, LRCLK, and SDATA.
However, the CS4205 does not require a connec-
tion to the asynchronous MCLK. The other three
signals are respectively received on ZSCLK, ZLR-
CLK, and ZSDATA. Although the ZV Port speci-
fication calls for SCLK running at 32 Fs, the
CS4205 supports any SCLK from 32 Fs up to
128 Fs. In all cases, only the first 16 bits of each
channel will be recovered from the incoming serial
data stream. Figure 21 shows the ZV Port format.
The ZV Port is controlled by the ZVEN, LOCK,
and Ph[24:0] bits in the ZV Port Control/Status
Registers (Index 6Eh, Address 0Eh - 0Fh).
Since the data received on the ZV Port is asynchro-
nous and at varying sample rates, it must be sample
rate converted before being sent to the digital mix-
er. The asynchronous SRC is similar in function to
the synchronous DAC SRC, but differs in the way
samples are received and how the sample rate is de-
termined. While the synchronous SRC is being pro-
grammed to the desired sample rate by the host and
requests samples from the host at the programmed
rate, the asynchronous SRC receives data from a
push source at an unknown rate. Therefore, the
asynchronous SRC must determine the rate of in-
coming data and calculate the necessary parame-
ters. The current sample rate can be determined
from the Ph[24:0] bits in the ZV Port Control/Sta-
tus Registers (Index 6Eh, Address 0Eh - 0Fh) by
Fs_in = Fs_out*Ph/16,777,216, where Fs_out is
48 kHz. Once the rate estimator has settled, the
LOCK bit will be asserted. If the incoming clock
rate changes, LOCK will be de-asserted until the
rate estimator has settled again. Settling may take
up to 400 ms. As long as the receiver is unlocked,
the ZV input to the digital mixer will be muted, re-
gardless of the state of the ZV mute bit in the Dig-
ital Mixer Input Volume Register (Index 6E,
Address 00h - 05h).
ZLRCK
ZSCLK
ZSDATA
Left Channel
Right Channel
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Figure 21. ZV Port Format (I²S, 16-bit data)
DS489PP4
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