Ac97 Audio Controller; Ac97 Link Bus - HP Deskpro EX Technical Reference Manual

Chapter 5 Input/Output Interfaces

5.8.2 AC97 AUDIO CONTROLLER

The AC97 Audio Controller is a PCI device (device 31/function 5) that is integrated into the 82801
ICH component and supports the following functions:
Read/write access to audio codec registers
16-bit stereo PCM output @ up to 48 KHz sampling
16-bit stereo PCM input @ up to 48 KHz sampling
Acoustic echo correction for microphone
AC'97 Link Bus
ACPI power management

5.8.3 AC97 LINK BUS

The audio controller and the audio codec communicate over a five-signal AC97 Link Bus (Figure
5-11). The AC97 Link Bus includes two serial data lines (SD OUT/SD IN) that transfer control
and PCM audio data serially to and from the audio codec using a time-division multiplexed (TDM)
protocol. The data lines are qualified by a 12.288 MHz BIT_CLK signal driven by the audio
codec. Data is transferred in frames synchronized by the 48-KHz SYNC signal, which is derived
from the clock signal and driven by the audio controller. The SYNC signal is high during the
frame's tag phase then falls during T17and remains low during the data phase. A frame consists of
one 16-bit tag slot followed by twelve 20-bit data slots. When asserted (typically during a power
cycle), the RESET- signal (not shown) will reset all audio registers to their default values.
BIT_CLK
(12.288 MHz)
SYNC
(48 KHz)
SD OUT
or SD IN
Slot
0
1
2
3
4
5
6-11
12
Figure 5-11. AC'97 Link Bus Protocol
5-26 Compaq Deskpro EX Series of Personal Computers
T1 T2
3
Codec
Bit 15 Bit 14 Bit 0
Ready
Slot 0
(Tag)
Description
Bit 15: Frame valid bit
Bits 14-3: Slots 1-12 valid bits
Bits 2-0: Codec ID
Command address: Bit 19, R/W; Bits 18..12, reg. Index; Bits 11..0, reserved.
Command data
Bits 19-4: PCM audio data, left channel (SD OUT, playback; SD IN, record)
Bits 3-0 all zeros
Bits 19-4: PCM audio data, right channel (SD OUT, playback; SD IN, record)
Bits 3-0 all zeros
Modem codec data (not used in this system)
Reserved
I/O control
First Edition – August 2000
T18 T19 T38
Bit 19 Bit 18 Bit 0 Bit 19 Bit 18
Slot 1
(Data)
T39 T58
Bit 0 Bit 19
Slot 2
(Data)