HMP9701 datasheet(3/20 Pages) INTERSIL

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Analog Mixer

The Analog Mixer generates two outputs, one stereo and

one mono. The stereo output is used to drive LINE_OUT and

is composed of a stereo mix of all analog input sources and

the audio output from the DACs. The mono output drives

MONO_OUT, and it is user selectable as either MIC only or

a mono mix of all the analog and PCM sources except the

PHONE and PC_BEEP inputs.

The inputs to the analog mixer pass through gain/attenu-

ate/mute (GAM) blocks. Each gain block provides volume

control from -34.5dB to +12dB in 1.5dB increments (see

Input Volume Registers 0Ch - 18h). Additionally, the GAM

blocks can be used to mute individual mixer inputs. An addi-

tional gain of 20dB is provided for the selected MIC input.

Note: for best SNR performance, the GAM block for the DAC

output should be used to control PCM analaog volume

rather than digitally attenuating the DAC PCM input to take

advantage of full resolution conversions.

Clocking

The HMP9701 derives it’s internal clock from an externally

attached 24.576MHz crystal. The crystal and 2 capacitors

are attached to the XTL_IN and XTL_OUT pins, and it

should be fundamental-mode/parallel resonant with a load

capacitor as speciﬁed by the crystal manufacturer (typically

12-30pF).

An external CMOS clock may be connected to XTL_OUT

instead of a crystal. If this external clocking option is used,

XTL_IN should be left ﬂoating. Please Note: No capacitors

are used on the crystal pins in this mode. For an example

circuit, refer to the Typical Application Schematic.

The HMP9701 divides the clock source by 2 to derive the

BIT_CLK provided to the companion digital controller. The

digital controller should divide the provided BIT_CLK by 256

to generate the 48kHz SYNC signal used to deﬁne the audio

frame transmitted over the serial digital interface (See Serial

Digital Interface Section)

Serial Digital Interface

Audio Data Format

The HMP9701 supports 16-bit 2’s complement linear PCM

data for record and playback. The 16-bit 2’s complement for-

mat (also called 16-bit signed format) is the standard method

of representing 16-bit digital audio. This format gives 96dB

theoretical dynamic range and is the standard for compact

disk audio players. This format uses the value -32768

(8000h) to represent minimum analog amplitude while

32767 (7FFFh) represents maximum analog amplitude.

Digital Serial Interface (AC Link)

The HMP9701 is linked to an AC’97 digital controller via a 5

pin digital serial interface as shown in Figure 1. This inter-

face, the AC-link, supports bidirectional, ﬁxed rate, serial

data streams. The data transfers are based on a time divi-

sion multiplexed (TDM) protocol that provides for multiple

input and output audio streams together with control and sta-

tus data. The AC-link protocol is based on incoming and out-

going audio frames which are each divided into 12 data slots

as shown in Figure 2. The HMP9701 allocates data slots for

2 PCM playback channels, 2 PCM record channels, codec

control, codec status, and a PCM microphone record chan-

nel. The remaining unused time slots are reserved.

SYNC

BIT_CLK

SDATA_OUT

SDATA_IN

RESET

HMP9701

AC’97

AUDIO

CODEC

FIGURE 1. HMP9701 CONNECTION TO AC’97 CONTROLLER

AC’97

DIGITAL

CONTROLLER

PCM

LEFT

RSRVD

MIC

RSRVD

PCM

RIGHT

STATUS

DATA

TAG

STATUS

ADDR

INCOMING

AUDIO STREAMS

PCM

LEFT

RSRVD

PCM

RIGHT

CMD

DATA

TAG

CMD

ADDR

OUTGOING

AUDIO STREAMS

SYNC

SLOT NO.

0123456789

TAG

PHASE

DATA PHASE

FIGURE 2. AC LINK BIDIRECTIONAL DATA FRAME

HMP9701

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