HMP9701 Intersil Corporation, HMP9701 Datasheet - Page 3

• Manufacturer Part Number: HMP9701
• Description: AC97 Audio Codec
• Manufacturer: Intersil Corporation

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)
AUDIO STREAMS
AUDIO STREAMS
OUTGOING
INCOMING
SLOT NO.
SYNC
PHASE
TAG
TAG
TAG
0
STATUS
ADDR
ADDR
CMD
1
STATUS
DATA
DATA
CMD
FIGURE 2. AC LINK BIDIRECTIONAL DATA FRAME
2
LEFT
LEFT
PCM
PCM
3
RIGHT
RIGHT
PCM
PCM
4
HMP9701
RSRVD
RSRVD
3
5
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.
FIGURE 1. HMP9701 CONNECTION TO AC’97 CONTROLLER
RSRVD
DATA PHASE
MIC
6
CONTROLLER
DIGITAL
RSRVD
RSRVD
AC’97
7
RSRVD
RSRVD
8
SDATA_OUT
SDATA_IN
BIT_CLK
RSRVD
RSRVD
RESET
SYNC
9
RSRVD
RSRVD
10
RSRVD
RSRVD
HMP9701
CODEC
AUDIO
AC’97
11
RSRVD
RSRVD
12