Philips DVDR985 Technical Training Manual page 55

axial (focus), and tangential directions (Tilt). This
access system consists of two parts, namely the
Focus Actuator and the Sled, which are, within a
certain range, mechanically and electrically inde-
pendent.
The analog signals from the SPIDRE are con-
verted into a digital representation using A/D
converters. The digital codes are then applied to
logic circuitry to obtain the various control sig-
nals.
OPC (Optimum Power Calibration)
This device has an integrated Optimum Power
Calculation block for use in CDR, CD-RW, and
DVD+R applications. It reads three analog sig-
nals: A1, A2, and CALF. These represent Max,
Min, and Average values of the EFM coming
from the disc, respectively. It also takes the
Power (PW) signal from the laser controller and
then feeds an analog signal, ALPHA0, out to
control the laser power. The conversion frequen-
cy is 88kHz per channel. Basically, the OPC pro-
cedure tries to find out the optimum laser power
to be used on a specific disc. It consists of three
phases:
1. WRITE - Random EFM data is written to
the test area of the disc at increasing levels of
laser power, controlled by ALPHA0.
2. READ - The data on A1, A2, and CALF is
read back from the test area and stored in mem-
ory.
3. CALCULATION - the embedded micro-
computer then calculates the setting of ALPHA0
where the least jitter is encountered. Some pre-
processing is carried out by the OPC logic to
reduce the processor's load. This sequence is
performed twice - first a coarse calibration, fol-
lowed by a fine-tuning.
The micro controller has many responsibilities. It
processes the Serial to Basic Engine, S2B, com-
mands from the Digital Board. It controls the var-
ious processes in the mechanism via I 2 C.
The MACE3 uses a Parallel communication bus
for access to its Flash ROM. Refer to Figure 29.
The Flash Memory contains the firmware for the
BE. The MACE3, the Encoder and AWSOME
share a parallel bus with 32K of SRAM
When the power is applied to the unit the Digital
Board sends a reset signal to the MACE3. The
MACE 3 checks its SRAM, the reads its Flash
Rom and sends a System Reset signal to the
ICs on the Servo Board. When its memory tests
are complete and they pass, a SUR control volt-
age goes low, indicating to the Digital Board that
it is ready to receive commands. It then initial-
izes its I Square C Bus and communicates to the
DROPPI and LADIC on the Mechanism. The Tilt
Motor is exercised and centered. The PSEN sig-
nal then appears.
The Microcomputer produces several outputs.
Many of them are error signals. It produces: the
Radial Error, the Focus Error, the Tilt Motor con-
trol, and the Position Control Sled (PCS) signals.
Each of the motors has a driver circuit.
The Microcomputer controls the Tray motor drive
circuit. The Tray switch goes directly to the
MACE3.
The Microcomputer controls the PCS. The
Position Control Sled must operate very accu-
rately. It cannot track the Disc's tracks of 1.6
microns alone, but its precision is a must. There
are two Hall sensors positioned 90 degrees apart
in a circular fashion. A round magnet is attached
to the armature of the drive motor. The position-
ing of the sensors gives them their name, Sin
and Cosine. The motor is a basic universal type.
The exact rotation of the armature is detected by
the Hall Sensors. The phase of the Hall sensor
signals are compared to a reference signal gen-
erated internally by the MACE3. The focus actu-
ator moves the lens side to side for tracking the
individual tracks. When the drive current to the
actuator increases to a certain point, the micro-
computer knows the Sled must be moved. The
Sled is driven to minimize the actuator's drive
current, meaning it is right under the proper
track. The microcomputer produces the
Reference DC offset for the Op amp inputs.