SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
In S/PDIF format, the digital signal is coded using the biphase-mark code (BMC). For each serializer transmitter n, the clock, frame, and data are embedded in only one signal - the data signal AXRn. In the BMC system, each data bit is encoded into two logical states (00, 01, 10, or 11) at the pin. These two logical states form a cell. The duration of the cell, which equals the duration of the data bit, is called a time interval. A logical 1 is represented by two transitions of the signal within a time interval, which corresponds to a cell with logical states 01 or 10. A logical 0 is represented by one transition within a time interval, which corresponds to a cell with logical states 00 or 11. In addition, the logical level at the start of a cell is inverted from the level at the end of the previous cell. Figure 24-115 and Table 24-326 show how data is encoded to the BMC format.
As shown in Figure 24-115, the clock frequency is twice the unencoded data bit rate. In addition, the clock is always programmed to 128 × fs, where fs is the sample rate (see Section 24.6.2.2.5.3, Frame Format, for details on how this clock rate is derived based on the S/PDIF format). The device receiving in S/PDIF format can recover the clock and frame information from the BMC signal.
Data (Unencoded) | Previous State at Pin AXRn | BMC-Encoded Cell Output at Pin AXRn |
---|---|---|
0 | 0 | 11 |
0 | 1 | 00 |
1 | 0 | 10 |
1 | 1 | 01 |