CS4297
CrystalClear™ SoundFusion™ Audio Codec ’97
tion in a new serial data frame is F0 and the last bit
position in the serial data frame is F255.
DIGITAL HARDWARE DESCRIPTION
AC’97 AC-Link
When SYNC goes active (high) and is sampled ac-
tive by the CS4297 (on the falling edge of
BIT_CLK), both devices are synchronized to a new
serial data frame. The data on the SDATA_OUT
pin at this clock edge is the final bit of the previous
serial data frame’s data. On the next rising edge of
BIT_CLK, the first bit of slot 0 is driven by the
AC’97 Controller on the SDATA_OUT pin. The
CS4297 latches in this data, as the first bit of the
frame, on the next falling edge of the BIT_CLK
clock signal.
The AC-Link is the serial connection between the
AC’97 Controller and the CS4297. The interface
consists of 5 signal lines (2 data, 2 clocks, and 1 re-
set). The basic connections of the link are shown in
Figure 2. The signals will be explained in detail be-
low.
AC-Link Protocol
The CS4297 serial interface is designed according
to the AC’97 Specification to allow connection to
any AC’97 Controller. An AC-Link audio frame is
divided into 13 ‘slots’; 1 16-bit slot and 12 20-bit
slots. During each audio frame, data is passed bi-di-
rectionally between the CS4297 and the AC’97
Controller.
DigitalAC’97
Controller
CS4297
SYNC
BIT_CLK
AC-Link Serial Data Output Frame
SDATA_OUT
For the serial data output frame, the SYNC,
BIT_CLK, and SDATA_OUT signals are used. In
the serial data output frame, data is passed on the
SDATA_OUT pin FROM the AC’97 Controller
TO the CS4297. In Figure 3 and in the following
Frame Slot definitions, the position of each bit lo-
cation within the frame is noted. The first bit posi-
SDATA_IN
RESET#
Figure 2. AC-link Connections
20.8uS
(48 KHz)
Tag Phase
Data Phase
SYNC
12.288 MHz
81.4 nS
BIT_CLK
Bit Frame
Position
F255
X
F0
F1
F2
F12
X
F13
X
F14
X
F15
X
F16
R/W
F36
F37
F56 F57
LP17 LP16
F76
F97
X
F255
X
Valid
Frame
Slot 1
Valid
Slot 2
Valid
WD15
WD14
RP17
SDATA_OUT
Bit Frame
Position
F255
0
F0
F1
F2
F12
0
F13
0
F14
0
F15
0
F16
0
F36
F37
F56 F57
F76
F97
0
F255
0
Codec
Ready
Slot 1
Valid
Slot 2
Valid
RD15
RD14
LC17
LC16
RC17
SDATA_IN
Slot 0
Slot 1
Slot 2
Slot 3
Slot 4
Slots 5-12
Figure 3. AC-Link Input and Output Framing
DS242F5
15
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