Kontron COMe Starterkit Eval T2 - Manual (Page 105)

COM Express Interfaces
2.15. Digital Audio Interfaces
The COM Express Specification allocates seven pins on the A-B connector to support digital
AC’97 and HD interfaces to audio Codecs on the Carrier Board. The pins are available on all
Module types. High-definition (HD) audio uses the same digital-signal interface as AC ’97 audio.
Codecs for AC ’97 and HD Audio are different and not compatible. Current Module chipsets
support HD Audio only.
Signal Definitions
Table 33: Audio Codec Signal Descriptions
Signal Pin Description I/O Comment
AC/HDA_RST# A30 CODEC Reset. O 3.3V
Suspend
CMOS
AC/HDA_SYNC A29 Serial Sample Rate Synchronization. O 3.3V
CMOS
AC/HDA_BITCLK A32 24 MHz Serial Bit Clock for HDA CODEC. O 3.3V
CMOS
AC/HDA_SDOUT A33 Audio Serial Data Output Stream. O 3.3V
CMOS
AC/HDA_SDIN0
AC/HDA_SDIN1
AC/HDA_SDIN2 B30
B29
B28 Audio Serial Data Input Stream from CODEC[0:2]. I 3.3V
Suspend
CMOS
The codec on a COM Express Carrier Board is usually connected as the primary codec with the
codec ID 00 using the data input line 'AC/HDA_SDIN0'. Up to two additional codecs with ID 01
and ID 10 can be connected to the COM Express Module by using the other designated signals
'AC/HDA_SDIN1' and 'AC/HDA_SDIN2'.
Connect the primary audio codec to the serial data input signal 'AC/HDA_SDIN0' and ensure that
the corresponding bit clock input signal 'AC/HDA_BITCLK' is connected to the AC'97/HDA
interface of the COM Express Module.
Clocking over the signal 'AC/HDA_BITCLK' is derived from a 24.576 MHz crystal or crystal
oscillator provided by the primary codec in AC97 implementations. The crystal is not required in
HDA implementations. This clock also drives the second and the third audio codec if more than
one codec is used in the application. For crystal or crystal oscillator requirements, refer to the
datasheet of the primary codec.
PICMG ® COM Express ® Carrier Board Design Guide Rev. 2.0 / December 6, 2013
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