Chapter 6. Theory of Operation
EK–MOL80–SV. B01
6–15
Data Buffer
The data buffer and associated control electronics provide a buffer to speed
match transfers to and from the host computer and the optical disk. The data
buffer provides a cache for read and write operations, optimizing the speed of
these transfers. The RWZ52 drive contains 512 Kbytes of buffer RAM.
Formatter/Sequencer
The formatter/sequencer function formats and decodes data for read and write
transfers. During a write function user data is sent via the SCSI bus. The for-
matter converts the parallel data into an encoded serial bit stream that includes
all the format and error correction features required to meet the ANSI and ISO
specifications. During reads, the decoder converts the serial data stream, which
includes format and error correction features, into parallel data.
Servo PCA
The servo PCA includes a digital signal processor (DSP) that controls the actions
of the many servo loops that interact with the optical head and the loader
assembly.
DSP Microprocessor and Support/Servo Control Loops
Most of the electronics on the servo PCA is analog circuitry. This circuitry is
designed into the control loops of the following servos: spindle motor/speed,
laser power control, track following, seek/position maintenance, focus actuation,
fine position actuation, and coarse position actuation. Whenever the drive is
performing a read or write operation, all these servos are activated.
