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S3C2440A RISC MICROPROCESSOR AC97 CONTROLLER
24-5
AC-LINK DIGITAL INTERFACE PROTOCOL
Each AC97 Codec incorporates a five-pin digital serial interface that links it to the S3C2440A AC97 Controller. The
AC-link is a full-duplex, fixed-clock, PCM digital stream. It employs a time division multiplexing (TDM) scheme to
handle control register access and multiple input and output audio streams. The AC-link architecture divides each
audio frame into 12 outgoing and 12 incoming data streams. Each stream has a 20-bit sample resolution and
requires a DAC and an analog-to-digital converter (ADC) with a minimum of 16-bit resolution.
SYNC
SDATA_OUT
SDATA_IN
Slot #
TAG
CMD
ADDR
CMD
DATA
PCM PCM
RSRVD
TAG
STATUS
ADDR
STATUS
DATA
PCM
LEFT
PCM
RIGHT
0123456789101112
RSRVDRSRVDRSRVDRSRVDRSRVDRSRVDRSRVD
RSRVD RSRVD RSRVD RSRVD RSRVD RSRVD RSRVD
PCM
MIC
LEFT RIGHT
Figure 24-4 Bi-directional AC-link Frame with Slot Assignments
Figure 24-4 shows the slot definitions supported by the S3C2440A AC97 Controller. The S3C2440A AC97
Controller provides synchronization for all data transaction on the AC-link.
A data transaction is made up of 256-bits of information broken up into groups of 13 time slots and is called a
frame. Time slot 0 is called as Tag Phase and it is 16-bits long. The remaining 12 time slots are called as Data
Phase. The Tag Phase contains a bit that identifies a valid frame and 12-bits that identify the time slots in the Data
Phase that contain a valid data. Each time slot in the Data Phase is 20-bits long. A frame begins when the SYNC
goes high. The amount of time the SYNC is high corresponds to the Tag Phase.
AC97 frames occur at fixed 48 KHz intervals and are synchronous to the 12.288 MHz bit rate clock, BITCLK. The
controller and the CODEC use the SYNC and BITCLK to determine when to send the transmit data and when to
sample the received data. A transmitter transitions the serial data stream on each rising edge of BITCLK and a
receiver samples the serial data stream on falling edges of BITCLK. The transmitter must tag the valid slots in its
serial data stream. The valid slots are tagged in slot 0. Serial data on the AC-link is from MSB to LSB. The Tag
Phase’s first bit is bit 15 and the first bit of each slot in the Data Phase is bit 19. The last bit in any slot is bit 0.
AC-LINK OUTPUT FRAME (SDATA_OUT)
SDATA_OUT
BIT_CLK
SYNC
AC '97 samples SYNC assertion here
AC '97 Controller samples first SDATA_OUT bit of frame here
END of previous Audio Frame
Valid
Frame
Slot(1) Slot(2)
Slot(12) "0" ID1 ID0 19 0
Tag Phase Data Phase
19 0
START of Data phase
Slot# 1
END of Data Frame
Slot# 12
48KHz
12.288MHz
Figure 24-5 AC-link Output Frame