Digital Interface - Compaq Armada e500 Series Reference Manual

Digital Audio Mode
Digital audio mode, shown in Figure 6-4, is a means of providing digital-ready audio
support. The final rendered audio can be routed to multiple locations. In the case of the
ES1921, the output of the playback mixer is routed to the ADC and back to the digital
controller, where the digital audio can be distributed. This audio data comes back to the
ES1921 through the AC-link and is passed through the DAC, through the DAC analog
volume control, to the Line_Out or True Line_Out volume controls, and then the
outputs. This is achieved by switching the digital audio mode bit. Set bit [6] of register
5Ch high to enable digital audio mode.
ES1921
AC-Link
Incoming
Audio Data
Playback Mixer
Volume Control
Figure 6-4. ESS1921 Digital Audio Mode Select Block Diagram

Digital Interface

The ES1921 uses a digital serial interface to link with a Maestro Digital Controller. This
link (the AC-Link) uses a bidirectional, fixed-rate, serial PCM digital stream. It carries
multiple input and output streams, as well as the control register information. To
achieve these, the AC-Link uses a time division multiplexed (TDM). Reference to
outgoing and incoming data streams (or time slots) are made from the point of view of
the Maestro Digital Controller. Therefore, an outgoing stream is sent from the Digital
Controller to the ES1921. An incoming stream is sent from the ES1921 to the Maestro
Digital Controller.
AC-Link Digital Serial Interface Protocol
Each audio frame of the digital serial stream is divided into 12 incoming and 12
outgoing data streams. The ES1921 implements 20-bit resolution within each data
stream.
Digital Audio
Mode Select
DAC
ADC
Record Source
and Select
Stereo
Outputs
Audio Subsystem 6-11