CS4294 Datasheet, PDF (10/42 Pages) Cirrus Logic – SoundFusion Audio/Docking Codec 97 (AMC 97)

CS4294
2. GENERAL DESCRIPTION
2.1 Overview
The CS4294 is a Mixed-Signal Audio Codec based
on the AC ‘97 1.0 Specification, and the AC ‘97
2.0 Extensions. It is designed to be paired with a
digital controller, typically located on the PCI bus.
The Controller is responsible for all communica-
tions between the CS4294 and the rest of the sys-
tem. The CS4294 functions as an analog mixer, a
stereo audio ADC, a stereo audio DAC, and a con-
trol and digital stream interface to the Controller.
The CS4294 contains three distinct functional sec-
tions: Digital, Analog Audio, and Extended Analog
Audio.
The Digital section includes the AC-Link registers,
power management support, SYNC detection cir-
cuitry, and AC-Link serial port interface logic. The
Analog Audio section includes the analog input
multiplexer (mux), stereo input mixer, stereo out-
put mixer, stereo ADCs, stereo DACs, and analog
volume controls. The Extended Audio section in-
cludes dual ADCs, dual DACs, GPIO control and
status, and power down and wake-up logic.
2.2 Modes of Operation
The CS4294 has two basic modes of operation.
Each mode allows varying functionality to meet a
wide variety of software and hardware configura-
tions. On power up or system reset, the device re-
verts to the basic configuration Mode 0. The four
channel expansion and enhanced digital docking
are activate in Mode 1.
2.2.1 Mode 0
This is the default operating mode for the CS4294.
It supports the legacy AC ‘97 audio modes of oper-
ation including audio mixer, ADC’s, and DAC’s.
2.2.2 Mode 1
Mode 1 is the four channel expansion mode. The
second ADC/DAC pairs are utilized for enhanced
audio functionality. The second stereo DAC’s are
routed to the alternate line audio outputs providing
2 additional audio channels. The secondary ADC
inputs may be connected to the output of the analog
stereo input mixer for enhanced audio effect pro-
cessing or enhanced digital docking in a note book
application.
3. DIGITAL SECTION
3.1 AC-Link
All communication with the Codec is established
with a 5-wire digital interface to the Controller chip
as shown in Figure 7. All clocking for the serial
communication is synchronous to the BIT_CLK
signal. BIT_CLK is generated by the primary Co-
dec and is used to slave the Controller and any sec-
ondary Codecs, if applicable. An AC-link audio
frame is a sequence of 256 serial bits organized into
13 groups referred to as ‘slots’. One frame consists
of one 16-bit slot and twelve 20-bit slots. During
each audio frame, data is passed bi-directionally
between the Codec and the Controller. The input
frame is driven from the Codec on the SDATA_IN
line. The output frame is driven from the Controller
SDATA_OUT line. Both input and output frames
contain the same number of bits and are organized
with the same ‘slot’ configuration. The input and
output frame have differing functions for each slot.
The Controller synchronizes the beginning of a
frame with the SYNC signal. In Figure 9 the posi-
tion of each bit location within the frame is noted.
The first bit position in a new serial data frame is F0
and the last bit position in the serial data frame is
F255. When SYNC goes active (high) and is sam-
pled active by the CS4294 (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
frame’s serial data. On the next rising edge of
BIT_CLK, the first bit of Slot 0 is driven by the
Controller on the SDATA_OUT pin. The CS4294
latches in this data, as the first bit of the frame, on
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