CS4298 Datasheet, PDF (12/52 Pages) Cirrus Logic – SoundFusion Audio/Modem Codec 97 (AMC 97)

CS4298
2. GENERAL DESCRIPTION
2.1 Overview
The CS4298 is a Mixed-Signal Audio/Modem Codec (AMC) 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 AMC Controller is responsible for all communications between the CS4298 and
the rest of the system. The CS4298 functions as an analog mixer, a stereo audio ADC, a stereo audio
DAC, a dual modem AFE, and a control and digital stream interface to the AMC Controller. The
CS4298 contains three distinct functional sections: Digital, Analog Audio, and Analog Modem.
The Digital Section includes the AC-Link registers, power management support, SYNC detection
circuitry, and AC-Link serial port interface logic. The Analog Audio section includes the analog in-
put multiplexor (mux), stereo output mixer, stereo ADCs, stereo DACs, and analog volume controls.
The Analog Modem section includes dual differential ADCs, dual differential DACs, analog loop-
back logic, GPIO control and status, and power down and wake-up logic.
2.2 Modes of Operation
The CS4298 has four basic modes of operation. Each mode allows varying functionality to meet a
wide variety of software and hardware configurations. On power up or system reset, the device re-
verts to the basic configuration Mode 0. The audio ADC’s and DAC’s functionality remains fixed
for each mode, but the modem ADC’s and DAC’s functionality changes per each configuration.
From a system perspective, the device can provide standard audio with modem, two line interface,
speakerphone, and four channel enhanced audio.
2.2.1 Mode 0
This is the default operating mode for the CS4298. It supports the legacy AC ‘97 audio modes of op-
eration including audio mixer, ADC’s, and DAC’s. The modem configuration supports a phone line
for modem ADC/DAC1 and a handset interface for modem ADC/DAC2.
2.2.2 Mode 1
This is the two phone line mode of operation. It is similar to mode 0 but the modem ADC/DAC2 is
interfaced to a second phone line in place of the handset.
2.2.3 Mode 2
This mode facilitates a full duplex speakerphone mode of operation. The ADC of modem
ADC/DAC2 is connected directly to the audio microphone in place of the handset or line 2 input.
This dedicated microphone capture path allows the host controller to implement echo cancellation
for hands free telephone operation. The modem DAC2 is not used in this mode.
2.2.4 Mode 3
Mode 3 is the four channel expansion mode. The modem ADC/DAC pairs are utilized for enhanced
audio functionality. The modem DAC’s are routed to the alternate line audio outputs providing 2 ad-
ditional audio channels. The modem ADC inputs may be connected to the output of the analog stereo
input mixer for enhanced audio effect processing or enhanced digital docking in a note book appli-
cation.
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