48.6.1.1 SPDIF Protocol

Data transmission complies with the IEC-60958 standard.

Data transmission is performed by the transfer of blocks of 192 frames.

Each frame is divided into two subframes, one for each channel.

Each subframe is divided into 32 time slots carrying the following fields:

• Preamble (4 bits)–There are three possible preambles named B, M and W. Preambles are specific patterns providing synchronization and identification of the subframes and blocks.
• Data (24 bits)–This field can carry a PCM audio data or any other information.
• Validity bit–This bit can be written to ‘0’ or to ‘1’ by the user with the VALIDx bit in the Mode register (SPDIFTX_MR).
• User data bit–User data may be used in any way required by the user. It is organized in a 192-bit block.
• Channel status bit–For every subframe, the channel status provides information related to the data carried in the main data field of that same subframe. It is organized in a 192-bit block.
• Parity bit–This bit ensures that time slots 4 to 31 carry an even number of ones and an even number of zeros.