WM9704CFT/V Wolfson Microelectronics plc, WM9704CFT/V Datasheet - Page 18

• Manufacturer Part Number: WM9704CFT/V
• Description: AMC97 Audio and Modem Codec
• Manufacturer: Wolfson Microelectronics plc

WM9704M
AC-LINK AUDIO OUTPUT FRAME (SDATA_OUT)
WOLFSON MICROELECTRONICS LTD
The datastreams currently defined by the AC’97 specification include:
Synchronisation of all AC-link data transactions is signalled by the WM9704M controller. The
WM9704M drives the serial bit clock onto AC-link, which the AC’97 controller then qualifies with a
synchronisation signal to construct audio frames.
SYNC, fixed at 48kHz, is derived by dividing down the serial clock (BIT_CLK). BIT_CLK, fixed at
12.288MHz, 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, (WM9704M 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 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, (the WM9704M for the input stream, AC’97 controller for the output stream), to stuff all bit
positions with 0s during that slot’s active time.
SYNC remains high for a total duration of 16 BIT_CLKs at the beginning of each audio frame.
The portion of the audio frame where SYNC is high is defined as the “Tag Phase”. The remainder of
the audio frame where SYNC is low is defined as the “Data Phase”. Additionally, for power savings,
all clock, sync, and data signals can be halted. This requires that the WM9704M be implemented as
a static design to allow its register contents to remain intact when entering a power savings mode.
The audio output frame data streams correspond to the multiplexed bundles of all digital output data
targeting the WM9704M’s DAC inputs, and control registers. As briefly mentioned earlier, each audio
output frame supports up to 12 20-bit outgoing data time slots. Slot 0 is a special reserved time slot
containing 16-bits, which are used for AC-link protocol infrastructure.
OUTPUT TAG SLOT (16-BITS)
Within slot 0 the first bit is a global bit (SDATA_OUT slot 0, bit 15) which flags the validity for the
entire audio frame. If the “Valid Frame” bit is a 1, this indicates that the current audio frame contains
at least one time slot of valid data. The next 12-bit positions sampled by the WM9704M indicate
which of the corresponding 12 time slots contain valid data.
Bit (15)
Bit (14)
Bit (13)
Bit (12:3)
Bit 2
Bit (1:0)
New definitions for Secondary Codec Register Access
PCM playback - 2 output slots
PCM record data - 2 input slots
Control - 2 output slots
Status - 2 input slots
Optional modem line codec output -
1 output slot
Optional modem line codec input -
1 input slot
Optional dedicated microphone input -
1 input slot
Frame Valid
Slot 1 Valid Command Address bit
Slot 2 Valid Command Data bit
Slot 3-12 Valid bits as defined by AC’97
Reserved
2-bit Codec ID field
2-channel composite PCM output stream
2-channel composite PCM input stream
Control register write port
Control register read port
Modem line codec DAC input stream
Modem line codec ADC output stream
Dedicated microphone input stream in support
of stereo AEC and/or other voice applications.
(Primary Codec only)
(Primary Codec only)
(00 reserved for Primary; 01, 10, 11
(Set to 0)
indicate Secondary)
PD Rev 3.2 January 2001
Production Data
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