User manual

Advantech SOM-Express Design Guide
Chapter 5 Carrier Board Design Guidelines 51
5.3 AC Link/Azalia interface
SOM-Express provides an AC Link/Azalia interface which is compliant to AC’97 Rev.
2.3 Specification and the Azalia Specification. Please establish the AC’97/Azalia
CODEC on the carrier board for your application.
5.3.1 Signal Description
Table 5.10 shows SOM-Express AC Link/Azalia interface signals, including pin
number, signals, I/0 and descriptions.
Table 5.10 Audio signals description
Pin Signal I/O Description
A30 AC_RST# O
AC link / Azalia : Reset output to AC97 CODEC, active low
A29 AC_SYNC O
AC link / Azalia : 48 kHz fixed-rate, sample-synchronization signal
to the CODEC(s)
A32 AC_BITCLK I/O
AC link: Bit Clock Input: This signal is a 12.288 MHz serial data
clock generated by the external codec(s). This signal has an
integrated pull-down resistor
Azalia: Bit Clock Output: This signal is a 24.000 MHz serial data
clock generated by SOM-Express. This signal has an integrated
pull-down resistor so that AC_BITCLK does not float when an
Azalia codec (or no codec) is connected but the signals are
temporarily configured as AC’97.
A33 AC_SDOUT O
AC link / Azalia : Serial TDM data output to the CODEC
B30,B29,
B28
AC_SDIN[0:2] I
AC link / Azalia : Serial TDM data inputs from up to 3 CODECs
5.3.2 Design Guidelines
Azalia is the next generation architecture for implementing audio, modem, and
communications functionality in the PC. The architecture of the SOM-Express Azalia-
link allows a maximum of three CODECs to be connected.
5.3.2.1 Connection of AC link and Azalia
5.3.2.2 AC link:
Figure 5-12 shows the connections for SOM-Express AC link signals.
Clocking is provided from the primary codec on the link via AC_BITCLK, and is
derived from a 24.576 MHz crystal or oscillator. Refer to the primary codec vendor for
crystal or oscillator requirement. AC_BITCLK is a 12.288 MHz clock driven by the
primary codec to the SOM-Express digital controller and to any other codec present.