USB Audio 2.0 Reference Design, XS1-L1 Edition Hardware Manual (1.0)
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3
USB Connector and Transceiver [B]
The board uses a standard USB series B receptacle as its USB connector. The
high-speed USB signals are connected to an SMSC® USB3318 USB transceiver which
provides a ULPI connection to the XS1-L1.
On power-up, a pulldown resistor holds the transceiver in reset until the XS1-L1 is
ready to begin accepting USB traffic. The USB transceiver reset pin is connected to
bit zero of port 32A so this can be controlled by software.
The transceiver uses the 13MHz clock provided by a discrete oscillator on the board
which doubles as the reference clock for the XS1-L1.
The I/O pins for the USB transceiver are mapped to ports on the XS1-L processor as
described in the port map shown later in this document.
4
Audio CODEC [C]
The board uses a 24 bit, 192kHz stereo audio CODEC (Cirrus Logic® CS4270).
The CODEC is configured to operate in stand-alone mode meaning that no serial
configuration interface is required. The digital audio interface is set to I
2
S mode with
all clocks being inputs (slave mode).
The CODEC has three internal modes depending on the sampling rate used. These
change the oversampling ratio used internally in the CODEC. The three modes are
shown below:
CODEC mode
CODEC sample rate range
Single speed
4-54kHz
Double speed
50-108kHz
Quad speed
100-216kHz
In stand-alone mode, the CODEC automatically determines which mode to operate in
based on the input clock rates.
The internal master clock dividers are set using the MDIV pins. MDIV1 is tied low
and MDIV2 is controlled by the L1 on bit 2 of port 32A.
With MDIV2 low, the master clock must be 256Fs in single speed mode, 128Fs in
double speed mode and 64Fs in quad speed mode. This allows an 11.2896MHz
master clock to be used for sample rates of 44.1, 88.2 and 176.4kHz.
With MDIV2 high, the master clock must be 512Fs in single speed mode, 256Fs
in double speed mode and 128Fs in quad speed mode. This allows a 24.576MHz
master clock to be used for sample rates of 48, 96 and 192kHz.
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