The DOBM signal (IEC958) can be directly
retrieved from the SAA7327 decoder (CD7 II).
This signal is indeed available on pin 51 of
the decoder.
More information on the DOBM signal provided
by the SAA7327 can be found in the decoder's
datasheet (downloads section).
The DOBM signal can then be sent to a
digital transformer before making it available
on an external connector. You can refer to the
following diagram to make your digital output.
However, a lot
of care should be taken when wiring the DOBM
to an external board : this digital signal can
indeed interfere with other signals,
especially in the HF section of the servo
board.
It is consequently advised to use shielded
cables for this signal.
DOBM signal can
also be created from I2S signals which are
available on connector CD901 : indeed, digital
audio transmitters can convert I2S to AES/EBU
(IEC60958) with very good performances :
Cirrus Logic's CS8402, Texas Instrument's
DIT4192 or AKM's AK4101 for instance.
Thus, the I2S to AES/EBU conversion can take
place on the audio printed circuit board,
which would match the EMC constraints,
preserve the integrity of the digital signal
and provide the best quality for an external
connection.
