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Intel® PXA255 Processor Developer’s Manual 13-3
AC’97 Controller Unit
13.4 AC-link Digital Serial Interface Protocol
Each AC’97 CODEC incorporates a five-pin digital serial interface that links it to the ACUNIT.
AC-link is a full-duplex, fixed-clock, PCM digital stream. It employs a time division multiplexed
(TDM) scheme to handle control register accesses and multiple input and output audio streams.
The AC-link architecture divides each audio frame into 12 outgoing and 12 incoming data streams.
Each stream has 20-bit sample resolution, but only 16-bit samples are supported in hardware. Each
stream requires a DAC or an analog-to-digital converter (ADC), both having a minimum 16-bit
resolution. The ACUNIT supports the data streams shown in Table 13-2.
Figure 13-1. Data Transfer Through the AC-link
nACRESET
SDATA_OUT
SYNC (48 kHz)
SDATA_IN_0
BITCLK (12.288 MHz)
AC’97 Controller Unit
AC’97 Primary CODEC
AC’97 Secondary CODEC
SDATA_IN_1
(ACUNIT)
AC-link
Table 13-2. Supported Data Stream Formats (Sheet 1 of 2)
Channel Slots Comments
PCM Playback Two output slots Two-channel composite PCM output stream
PCM Record data Two input slots Two-channel composite PCM input stream
CODEC control Two output slots Control register write port
CODEC status Two input slots Control register read port
Modem Line
CODEC Output
One output slot Modem line CODEC DAC input stream
Modem Line
CODEC Input
One input slot Modem line CODEC ADC output stream