17-18
MCF5249UM
MOTOROLA
Digital Audio Interface (EBU)
As previously mentioned, packet sync extraction is tolerant for single-symbol errors. Packet sync detection
is based on the recognition of the sequence data-sync-sync-data in the symbol stream, because this is the
only syncing sequence that is not affected by single errors. If the sync symbol is not found 98 symbols after
the previous occurrence, it is assumed to be destroyed by channel error, and a new sync symbol is
interpolated.
Normally, only data bytes are passed to the application software. Every data byte will have its most
significant bit set. If sync symbols are passed to the application software (i.e., the processor), they are
seen as all-zero symbols. Sync symbols can only end up in the data stream due to channel error.
17.3.1.10
Behavior of User Channel Receive Interface (non-CD data)
This section details the behavior of the user channel receive interface on incoming non-CD data.
This mode is selected if UsyncMode (bit 1) in register CD Text control is set ‘0’.
In non-CD mode, the IEC958 User channel stream is recognized as a sequence of data symbols. No
packet recognition is done.
Any sequence found in the IEC958 U-channel stream starting with a leading one, followed by 7 information
bits, is recognized as a data symbol. Subsequent data symbols are separated by pauses. During the
pause, zero bits are seen on the IEC958 U-channel.
Four consecutive data symbols seen in the IEC958 U-Channel stream are grouped together into the
UChannelRcv register. First symbol is left, last symbol is right aligned. Whenever UChannelRcv contains 4
new data symbols, UChannelRcvFull is asserted.
In this mode, the operation of QchannelRcv and associated interrupt QChannelRcvFull is reserved,
undefined. Also reserved, undefined is the operation of ChannelLengthError and ChannelSyncFound.
The U-channel is extracted and output by the IEC958 Receive block on EBURcvUChannelStream.
17.3.2
IEC958 TRANSMIT INTERFACE
The IEC958 interface provides the necessary features to allow transmitting of digital data according to the
IEC958 specification with the exception that only 20-bit data is supported. The 4 LSB’s of the 24-bit data
word are always ‘0’. In addition to data, the interface allows for transmission of the C- and U-channels and
control over the Valid flag. The transmitter has 2 physical outputs. One with Consumer C-Channel format
and one with ‘Professional’ C-Channel format. On the U-channel, only the CD User Data format is
supported.
Note: EBUOUT1 and EBUOUT2 will output a clock signal just after reset and before they
can be configured as GPIO. The frequency of the clock output will be CRIN/16.
17.3.2.1
Transmit “C” Channel
There are two IEC958 outputs. The difference is the formatting of the “C” channel. There are also two
IEC958 “C” channel control registers, EBU1TxCChannel1 and EBU1TxCChannel2. The following tables
show the formatting of both IEC958 outputs.
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