ASAHI KASEI
[AK4101A]
n 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.
Channel 1 W Channel 2 B Channel 1 W Channel 2 M Channel 1 W Channel 2
M
Sub-frame
Frame 0
Figure 14. Block format
Sub-frame
Frame 191
Frame 1
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.
0
3 4
27 28 29 30 31
L
S
B
M
Sync
Audio sample
S V U C P
B
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
11101000
Preceding state = 1
00010111
B
M
W
11100010
11100100
00011101
00011011
Table 6. Sub-frame preamble encoding
MS0250-E-00
2003/07
- 19 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
