17-22
MCF5249UM
MOTOROLA
Digital Audio Interface (EBU)
if(UChannelTxEmpty interrupt) then
if(UChannelTxNextFirstByt interrupt set also) then
reset this interrupt
synchronize pointer to sent out new frame
end if ;
load UChannelTransmit with data from pointer
update pointer
reset interrupt
end if ;
17.3.3.1
Free Running Counter Synchronization
There is a synchronization issue on start-up between the MCF5249 and some channel encoders. On
start-up, the RCK clock is kept silent. At a certain point in time, the CDR601 will start clocking the RCK, and
then it will require that the first symbol transmitted from the MCF5249 to the CDR60 is a sync symbol. If
this is not the case, the CDR60 fails to synchronize.
To solve the synchronization issue, the counter that determines the sync position can be preset using the
17.3.3.2
Controlling the SFSY Sync Position
When RCK is not clocking, it is possible to control the subcode byte number that will be sent out next by
the CD-Subcode interface by writing CdTextControl with PresetEn set ‘1’.
When 0 is written to presetCount, the next byte sent out will be a CD-Subcode sync byte. (SFSY low).
When a value (97 - i) is written to presetCount, i non-sync bytes are transmitted, followed by a sync
byte.
After writing to CdTextControl with PresetEn set to ‘1’, next bit out will always be the first bit of a new
byte.
Writing CdTextControl with PresetEn set to ‘1’, while RCK is running, will result in unpredictable,
undefined operation.
17.3.4
INSERTING CD USER CHANNEL DATA INTO IEC958 TRANSMIT DATA
Source selection of data transmitted into the User Channel of IEC958 transmitter is selected by bits (1,0) of
register EBUConfig.
When selected source is IEC958 receiver, every user channel data byte received into the input
IEC958 user channel, is inserted into the outgoing stream at approximately. the same time it was
found in the incoming stream.
When selected source is CD-Subcode, every data byte transmitted over the CD-Subcode output is
also inserted into the IEC958 out stream. The most significant bit of every byte is transmitted as a “1”.
All sync symbols are transmitted as all-0.
In case RCK clock is not present, it is still possible to use the CD-Subcode interface to assemble the
outgoing IEC958 User channel data. In this case, bit UChanTxTim in register CDText config must be
set ‘1’ (see
Table 17-38). It will cause the timing to the CD-Subcode registers to be controlled by the
IEC958 transmitter. One symbol (data or sync) will be transmitted into the IEC958 output every 12
User Channel data bits.
1. CDR60 is the informal name for Philips CD-R channel encoder
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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