CMI9738 Datasheet, PDF (10/36 Pages) List of Unclassifed Manufacturers – Integrated Multi-channel AC97

CMI 9738
Integrated Multi-channel AC‘97
4.4 AC-LINK DIGITAL SERIAL INTERFACE PROTOCOL
The CMI9738 communicates to the AC'97 controller via a 5-pin digital serial AC-Link
interface,which is a bi-directional, fixed rate, serial PCM digital stream. All digital audio streams,
commandsand status information are communicated over this point-to-point serial interconnect.
The AC-Linkhandles multiple inputs, and output audio streams, as well as control register
accesses using a timedivision multiplexed (TDM) scheme. The AC'97 controller synchronizes all
AC-Link data transaction.The following data streams are available on the CMI9738
SDATA_OUT TAG
SDATA_IN TAG
Status (STATUS ADDR & DATA) read port
PCM L & R DAC Playback
PCM L & R ADC Record
1 output slot (0)
1 input slot (0)
2 input slots (1,2)
2 output slots (3,4)
2 input slots (3,4)
Figure2. AC ‘97 Standard Bi-directional Audio Frame
Synchronization of all AC-Link data transactions is handled by the AC'97 controller. The
CMI9738 drives the serial bit clock onto AC-Link. The AC'97 controller then qualifies with a
synchronization signal to construct audio frames.
SYNC, fixed at 48 kHz, is derived by dividing down the serial bit clock (BIT_CLK). BIT_CLK,
fixed at 12.288 MHz, provides the necessary clocking granularity to support 12, 20-bit outgoing
and incoming time slots. AC-Link serial data is transitioned on each rising edge of BIT_CLK. The
receiver of AC-Link data, CMI9738 for outgoing data and AC'97 controller for incoming data,
samples each serial bit on the falling edges of BIT_CLK.
The AC-Link protocol provides for a special 16-bit (13-bits defined, with 3 reserved trailing bit
positions) time slot (Slot 0) wherein each bit conveys a valid tag for its corresponding time slot
within the current audio frame. A “1” in a given bit position of slot 0 indicates that the
corresponding time slot within the current audio frame has been assigned to a data stream, and
contains valid data. If a slot is “tagged” invalid, it is the responsibility of the source of the data
(CMI9738 for the input stream, AC'97 controller for the output stream) to stuff all bit positions
with 0’s during that slot’sactive time.
C-MEDIA Electronics Inc.
6F, 100, Sec. 4, Civil Boulevard, Taipei, Taiwan, R.O.C. 106
TEL: [phone] FAX: [phone] E-mail:[e-mail]
Revision Date Apr./2002
Revision 1.1