Cirrus Logic AN22 - Manual (Page 4)

AN22
4 AN22REV2
Table 1 lists the preamble biphase-mark data pat-
terns and what each designates. Since bi-
phase-mark encoding is not polarity conscious,
both phases are shown in the table. Preambles "X"
and "Y" indicate a sub-frame containing
channels A and B respectively. Preamble "Z" re-
places preamble "X" once every 192 frames to in-
dicate the start of a channel status block.
There are two channel status blocks, one for
channel A and one for channel B. Since there are
192 frames in a block, each channel has a channel
status block 192 bits long. These 192 channel sta-
tus bits in a block can be arranged as 24 bytes. The
blocks have one of two formats, professional or
consumer. The first bit of the channel status block
defines the format with 0 indicating consumer and
1 indicating professional.
Channel Status Block - Professional Format
Setting the first bit of channel status high desig-
nates the professional or broadcast format. The
channel status block structure for the professional
format is illustrated in Figure 5 and shows bit 0 of
byte 0, PRO, to contain a one. Tables 2 and 3 list
the bits in each byte and their meaning. The areas
designated "reserved" in the figures and tables, are
currently not specified and must be set to 0 when
transmitting. Most of the professional format data
was obtained from the AES3-1985 document, and
information from AES3-199x. Since the AES spec-
ification is currently being updated, the accuracy of
this data is not guaranteed.
BYTE 0
bit 0 PRO = 1
0 Consumer use of channel status block
1 Professional use of channel status block
bit 1 Audio
0
Normal Audio
1 Non-Audio
bits 2 3 4 Encoded audio signal emphasis
0 0 0 Emphasis not indicated. Receiver
defaults to no emphasis with manual
override enabled
1 0 0 None. Rec. manual override disabled
1 1 0 50/15
µ
S. Rec. manual override disabled
1 1 1 CCITT J.17 . Rec. man. override disabled
X X X All other states of bits 2-4 are reserved
bit 5 Lock: Source Sample Frequency
0 Locked - default
1 Unlocked
bits 6 7 Fs: Sample Frequency
0 0 Not indicated. Receiver default to 48 kHz
and manual override or auto set enabled
0 1 48 kHz. Man. override or auto disabled
1 0 44.1 kHz. Man. override or auto disabled
1 1 32 kHz. Man. override or auto disabled
BYTE 1
bits 0 1 2 3 Channel Mode
0 0 0 0 Mode not indicated. Receiver default to
2-channel mode. Manual override enabled
0 0 0 1 Two-channels. Man. override disabled
0 0 1 0 Single channel. Man. override disabled
0 0 1 1 Primary/Secondary (Ch. A is primary)
Manual override disabled
0 1 0 0 Stereophonic. (Ch. A is left)
Manual override disabled.
0 1 0 1 Reserved for user defined application
0 1 1 0 Reserved for user defined application
1 1 1 1 Vector to byte 3. Reserved
X X X X All other states of bits 0-3 are reserved.
bits 4 5 6 7 User bits management
0 0 0 0 Default, no user info indicated
0 0 0 1 192 bit block structure
Preamble ‘Z’ starts block
0 0 1 0 Reserved
0 0 1 1 User defined application
X X X X All other states of bits 4-7 are reserved.
Table 2. Professional Channel Status bytes 0-1.