Editing AC'97 (section)

==AC-Link==
The AC-Link is a digital link that connects the DC97 (the controller) with the audio "codecs." It is composed of five wires: the 12.288&nbsp;MHz {{var|clock}}, a 48&nbsp;kHz {{var|sync}} signal, a {{var|reset}} signal, and two data wires which carry the actual audio data: {{var|sdata_out}} and {{var|sdata_in}}. The first four are outputs from the controller, while {{var|sdata_in}} carries input from the codec. The link carries a bidirectional serial data stream at a fixed bitrate (12.288&nbsp;Mbit/s) between the controller and one or more codecs.

Each 12.288&nbsp;Mbit/s stream is divided into 256-bit frames (frame frequency is 48&nbsp;kHz). This is therefore a [[time-division multiplexing]] scheme.

Every frame is subdivided in 13 slots. The first (slot 0) is 16 bits long and contains validity flags for the remaining slots, while the remaining 240 bits are divided in twelve 20-bit slots (slots 1–12), used as data slots.

Slots 1, 2 and 12 are used for non-audio data, while slots 3&ndash;11 carry up to nine channels of raw [[pulse-code modulation]] audio signals. Normally, six channels are used for 5.1 surround sound, and three channels are available for modem use. However, slots can be combined to provide a 96&nbsp;kHz sampling rate for the L, R and C channels.

Lower sample rates (such as 44.1&nbsp;kHz) are implemented using a [[Handshake (computing)|handshake protocol]] between the controller and codec which skips data during certain frames. (This capability depends on the codec. Alternatively, [[sample rate conversion]] could be performed in the DC97 (controller) or in the software driver.)