Philips CDR880 - Page 57

BASICS CDR/RW
11
et
UIT
On the more extended overall blockdiagram most important
components are shown again. The electrical signal flow of the
recording signal from the analogue input on the connector
board is as follows:
- the analogue recording level is adjusted on the level board
and then
- the A/D conversion (ADC) to 7S format (datapath);
- the Digital Audio Input (DAI-O) and General Digital Input
(GDIN) are inserting the coaxial and optical input signals
which are converted into IS format (datapath), from
Datapath the signals are sent to
- the Compact Disc CIRC-EFM Encoder Plus (CDCEP) which
encodes the signal into EFM, then the signal is lead to
- CDM Board with the Laser & timing unit and on
- CDMS36 the Laser Driver Unit is processing the signal onto
the disc. The processing of all these activities is mastered by
- the System Controller. The servo drivers on the CDM
board are driven by commands from
- Servo Microcontroller and
the scanning of input keys is processed by the slave uP
on the display board.
The analogue inputs are pre-amplifiers which adapt the
signal level to the operational level. Adjustments can be done
about the recording level. Prevent over-amplification of the
analogue signal because clipped audiosignals are registered
as mutes and are "damaging" the recording quality. For that it
is better to have a "safe" input level. After that the analogue
audio signal will be converted in ADC into the 17S format.
The digital input from the IEC958 standard format with data
in Biphase marked code needs no adjustment and will be
transferred into the I7S format too by GDIN. The subcode
information of the digital input signal will be processed to the
subcode information for the new CD-R or CD-RW disc.
The 7S signal is converted into the CIRC/EFM format in the
CDCEP encoder. Each input audiosignal is worked up to the
EFM format which will be written on the disc via the Laser &
Timing device on the CDM board and laser device unit on
the CD mechanism CDM36.
In case both inputs (analogue and digital) are supplying
signals, preference is given to the digital input source.
The digital input, but also the Ps signal from the analogue
input, are connected to DAI-O which caiculates a new digital
output signal. Via the IS signal to the DAC IC the analogue
output signal is also available. So for monitoring both digital
and analogue output signals can be used.
On the Main board the "User" pProcessor (System Controller),
scans via the slave pProcessor the keyboard for commands
from the user. After that the user uP executes that command.
The user pP or System Controller is the heart of the set.
It co-ordinates ail functions within the set. The writing process
in the CDR-loader is controlled by the components on the
CDM Board. This board consists of a.o. a laser contro! and
timing device. On this board the reading and writing moments
are started and the laserdiode will be actuated at correct level
(reading CD, reading CD-RW, writing CD-R, writing CD-RW)
and the laserlight will be processed onto the disc.
During the writing operation the wobble processing device
takes care for the track following of the pregroove. This is
done during the reading moments. At the same time the disc
rotation is controlled via the ATIP-pregroove wobble informa-
tion. As long as the recording disc is not finalized the ATIP
information is processed for controlling CDM, even in
playback mode.
When reading a conventional or finalized disc the driver
control is switched to the well-known EFM-motorcontrol
(MOTO 1/2) and the wobble processing is switched off.
On the CDM Board there is also the AEGER IC (Analogue
Error signal Generator for Erasable and Recordable CD) with
a normalizer circuit. This internal circuit amplifies all signals
from the Light Device Unit to the same average level as the
total reflected signal. By this adaption all photodiode signals
are brought to a "normal" level. Now servo signals like
Focus-error, Radial-error can be processed better. Even the
HF-signal will be equalized in the AEGER.
The parts that provide output signals are in principal the same
stages as known from the conventional CD-player where the
EFM signal is recovered into the audiosigna!:
- the CIRC-EFM decoder (CD60) decodes to °s datapath
bus format, from this to
- the D/A conversion (DAC).
- the digital outputs are received from CD60.
- the analogue output from DAC.
Notice that the signal available for monitoring in the recording
mode is not the recorded signal but it is only the input Ps signal
which can be controlled. In case the original input signal is an
analogue input this signal can activate automatic track incre-
ment. If the output level via the internal monitor indicates a sig-
nal below -60 GB, the next track will be generated. In the digital
input mode the subcode information indicates the next track.
There is no need to say that all these functions are processed
by a system microprocessor software program on the MAIN
Board.
In the following an example of the use of a recording disc
and a short description of the activities in the recorder.
After that the power on and open tray keys have been acti-
vated, the unrecorded disc (e.g. CD-R) will be put on the tray.
Close the tray and the information on the area of the lead-in
will be read. Because it is an unrecorded disc there is no infor-
mation in the lead-in. Now the spot has been moved under
the PMA area and the system controller switches over to
so-called "ATIP-mode", pregroove information. The brand-new
disc has not been recorded before so there is no information
too. In the pregroove the recorder finds a recommended
Optical Power Calibration value. Now this recommended
power is taken as the middle of the 15 steps to make a test
recording on the pregroove in the Power Calibration Area of
the disc.
After recording, the written value is being read. If the intensity
of the reading signal corresponds with a calibrated value the
power ok sign is indicated and the corresponding OPC-value
is stored. (See paragraph 3.2.2.2.) If after one run the ideal
value is not found the next 15 steps are written on the disc.
This procedure can be repeated 4 times. All figures of the
disc are stored in the memory of the microprocessor.
After this OPC procedure, one can decide to make a
recording of a piece of music. This will be written in the first
track, "under" the pregroove on the reflection layer of the disc
in the recording layer area.
gS PH | LI PS Service disc systems