[AK4101A]
MS0250-E-01 2012/11
- 19 -
Data Transmission Format
Data transmitted on the TX outputs is formatted in blocks as shown in
Figure 14. Each block consists of 192 frames. A
frame of data contains two sub-frames. A sub-frame consists of 32 bits of information. Each data bit received is coded
using a bi-phase mark encoding as a two binary state symbol. The preambles violate bi-phase encoding so they may be
differentiated from data. In bi-phase encoding, the first state of an input symbol is always the inverse of the last state of
the previous data symbol. For a logic “0”, the second state of the symbol is the same as the first state. For a “1”, the
second state is the opposite of the first.
Figure 15 illustrates a sample stream of 8 data bits encoded in 16 symbol states.
Frame 191 Frame 0 Frame 1
Sub-frame Sub-frame
M
Channel 1 W Channel 2 B Channel 1 W Channel 2 M Channel 1 W Channel 2
Figure 14. Block format
0 1 1 0 0 0 1 0
Figure 15. A biphase-encoded bit stream
The sub-frame is defined in
Figure 16 below. Bits 0-3 of the sub-frame represent a preamble for synchronization. There
are three preambles. The block preamble, B, is contained in the first sub-frame of Frame 0. The channel 1 preamble, M,
is contained in the first sub-frame of all other frames. The channel 2 preamble, W, is contained in all of the second sub-
frames.
Table 6 below defines the symbol encoding for each of the preambles. Bits 4-27 of the sub-frame contain the 24 bit
audio sample in 2’s complement format with bit 27 as the most significant bit. For 16 bit mode, Bits 4-11 are all 0. Bit
28 is the validity flag. This is “H” if the audio sample is unreliable. Bit 29 is a user data bit. Frame 0 contains the first
bit of a 192 bit user data word. Frame 191 contains the last bit of the user data word. Bit 30 is a channel status bit.
Again frame 0 contains the first bit of the 192 bit word with the last bit in frame 191. Bit 31 is an even parity bit for bits
4-31 of the sub-frame.
Sync P
C
UV
L M
S Audio sample S
B B
0 3 4 27 28 29 30 31
Figure 16. Sub-frame format
The block of data contains consecutive frames transmitted at a state-bit rate of 64 times the sample frequency, fs. For
stereophonic audio, the left or A channel data is in channel 1 while the right or B data is in channel 2. For monophonic
audio, channel 1 contains the audio data.
Preamble Preceding state = 0 Preceding state = 1
B 11101000 00010111
M 11100010 00011101
W 11100100 00011011
Table 6. Sub-frame preamble encoding
