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1.7
TECHNICAL APPENOIX
1.7.1
Oigi~al
outputs
The
two unbalanced outputs DIGITAL OUTPUT 1 and 2 [28)
as
well as the balanced output 00 [29J supply the
comp-
Lete information of the CO in digital form.
In
addition
to the music data
of
the two channels, all subcode Infor-
mation is output serially. This means that the whole con-
tent of a CO-ROM is available via these outputs.
Jhe two unbalanced outputs [281 are connected in paralLel
and are electricaLly isolated from the other circuitry by
an isolation transformer
.
The
same information as on the unbalanced output is also
available
on the balanced output [291
.
This
output
is
also electrically isolated from the other circuitry by an
isoLation transformer.
1.7.2
Digital data format
The data of the digitaL outputs are transmitted serial-
ly
in the lEe format with a nominal FRAME
freQuency
of
44
.
1
kHZ
(identicaL to the scanning frequency;
in
vari-
speed mode the fRAME frequency changes
correspondingly).
Ea~h
FRAME consists of two 32-bit SUBFRAMES (one SU8FRAME
each
for the left-hand and the right-hand
channel).
In
time
division
mUltiplex transmission this results in
a
data
volume of 2 ' 32 bits· 44
.
1
kHz
=
2822.4
kbits/s.
The
FRAMES are arranged
in
blocks comprising 192 fRAMES
each
.
( XI
(Y)
(ll
(Y)
(X)
(0
SUB
<-
FRAME
192
->
11
<-
FRAME
->11
<-
fRAME
2
END Of BLOCK A
->U<-
ST~RT
OF BLOCK B
SUBFRAME:
A SUBFRAME contains a SYNC PREAM8LE (0
.
.. 3), suppLemen-
tary information AUX
(4 ... 7),
the audio information AUDIO
SAMPLE
WORO
(8 .
.
. 27)
in linear two's complement
repre-
sentation, a VALIDITY FLAG (28),
t~o
data channels U (29)
and
C
(30) as well as a PARITY BIT (31).
o
3
4
7 8
27
28
31
SYNC
IL
M
PREAMBLE
S
AUX
IS
AUDIO SAMPLE WORD
S
vue
P
8
IS
B
,
,
A727
E 1111
CodinQ:
Except
for the SYNC PREAMBLE the data are
transmitted
in
biphase format
.
One bit consists
01
two CLOCK cycles
.
A new bit always changes the state of the data line.
For
logic
"0"
toe status
is
not thanged for the bit duration,
for logic
"1"
it changes with the second CLOCK
.
Clock
(2 times bit
rate)
~~
Source coding
(hanne l cod
i
ng
(bipha5€ mark>
o
o
o
SYNC PREAMBLE
:
This first part of
a
SUBFRAME
is used for
synchroniza-
tion
and
identification of the SU8FRAME or
blOCk
.
For
transmitting an 8-bit word withIn these four bits
and
to
ensure
that
no data bit can imitate the
preamble,
the
biphase format
is
violated and a
bit
is
transmitted
with
each CLOCK.
Valid are the three preambles B,
ing
on toe preceding bit (PARITY
such
a
way
that the status for
changes with the first bit of the
M, and
~
which, depend-
81T),
are selected
in
the
data
line
aLways
SYNC PREAMBLE.
~-
U~~Clock
~~I~lJ
I
I
IPARITY
LJlJL--
r -
---r--
lSB
Lack
of
transition at
bit
boundary
PREAMBLE "M"
:
1110 0010
Last line status
Il
-
SYNC-PREAMBLE "B"
(Z
)
1110
1000
0001 0111
SYNC-PREAMBLE
"M"
(X)
1110 0010
0001 1101
S~NC-PREAMBlE
ow'
(Y}
1110 0100
0001 1011
The SYNC PREAMBLE "8" marks the start of a block and
the
start of the SU8FRAME "channell".
The
SYNC
PR~AMBLE
"M" marks the start of
the
SUBFRAME
"channel 1'.
The
SYNC
PREAMBLE "W" marks the start of
the
SUBFRAME
"channel 2"
.
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