Digital Audio Interface (EBU)
MOTOROLA
Audio Functions
17-21
17.3.3
CD SUBCODE INTERRUPTS
The following interrupts are associated with the CD Subcode data:
UChannelTxEmpty — Register is empty, needs re-load.
UChannelTxUnderrun — Underrun error on register.
UChannelTxNextFirstByte — Received indication from CD-Subcode output interface that next word
to be written contains first byte of the 96-byte U-channel frame.CD Subcode Interface: SFSY, RCK
and SUBR
Note: The subr, rck, and sfsy signals are only used on the 160 MAPBGA package.
Figure 17-5 Data Format on CD-Subcode Interface Out
RCK is the incoming clock from the channel encoder. SFSY is used to flag the first symbol bit, and first
packet symbol. During the first bit of every symbol, SFSY is low, During the first two bits of the first symbol
of every packet, SFSY is low.
SUBR is the data out, used to transmit outgoing data in serial form. The most significant bit is transmitted
first.
Note: The SUBR, RCK, and SFSY signals are only used on the 160 MAPBGA package.
RCK is an input, SFSY and SUBR are outputs.
CD User channel subcode is transmitted out of the 3-wire CD subcode interface. This user channel
subcode needs to be assembled by the ColdFire processor application software.
The CD-Subcode format has a 98-symbol packet structure. Of these 98 packets, the first 2 symbols are
sync symbols, followed by 96 8-bit data symbols.
The boundaries of the 98-symbol packets are determined by free-run counters. The first symbol of any
packet is transmitted with the special sync sequence on SFSY. The first and second symbols are all-0
symbols. The other 96 symbols need to be uploaded by the application software in register
UChannelTransmit.
Upload is done by application software handshaking to interrupt UChannelTxEmpty. If this interrupt is set,
the application software uploads 4 symbols of the current user channel packets into register UChannelTx.
The interrupt UChannelTxNextFirstByte flags the start of a new U channel packet. It is always coincident
with UChannelTxEmpty, and signal that the first 4 symbols of a new packet need to be loaded into
UChannelTx.
The following pseudo-code reacts on both interrupts. One interrupt handler can take care of both
UchannelTxEmpty and UChannelTxNextFirstByte. This last interrupt is not enabled.
RCK
SFSY
SUBR
(MCF5249 in)
(MCF5249 out)
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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