Grass Valley PDR 200 Service Manual - Manual (Page 36)

Chapter 3 Theory of Operation
3-4 PDR 200 Service Manual
For recording, JPEG CODEC chips on the Disk Controller (or Controllers) compress
the output of the Video Router and the Controller(s) then route the output for storage
on the Media Hard Disk array. The Media Hard Disk array uses an Ultra SCSI-2 bus
to communicate between the Media Hard Disks and the Disk Controller(s).
For playback, parallel video is decompressed and output to the Video Router. This
Video Router directs the parallel digital video signal to either the optional serial Mix
Effects circuit board, for more processing before the signal is output, or routes the
signal directly to the Video Output section of I/O circuitry.
Video Recording System
Video synchronization, through the PDR 200, requires a reference, either internal
(from the video input) or from an external reference. External genlock is to a reference
color black or composite sync. The Reference Genlock outputs a 27 MHz video clock
and a Field Reference signal that is used throughout the system. The Reference
Genlock also provides the I/O for longitudinal time code.
The CCIR 601-2 signal, output from the Video I/O, is input to the Video Router,
which is a 32-by-32 cross-point matrix with 8-bit inputs and outputs. Video Router
outputs include the Effects inputs, the EDR inputs, and the Video Output. The Effects
circuitry, which provides production switching capability, consists of a 6-input and
2-output configuration, controlled by the system processor.
The Master Enhanced Disk Recorder (MEDR) has two compression/decompression
channels. The JPEG compression algorithm is applied one field at a time. Each
channel is bidirectional for either encoding or decoding. Video data sampling is
synchronized to CCIR-601 Start-of-Active Video (SAV) and only active pixels are
compressed and stored. Parallel digitized video is routed over a SCSI-2 fast wide bus
to and from the Media Hard Disks. Video, for output, is sent in 8-bit parallel
component format to the Video Router.
Software controls the entire recording/playback operation. The system processor,
with its independent Hard Disk program storage, controls all operations through the
EISA bus. The System Hard Disk contains the Windows NT operating system and
application-specific software. The Processor can be controlled through the RS-422
Interface, which provides up to eight individual ports, or with the keyboard and
mouse. A VGA Interface is included to drive a SVGA monitor (optional), which
provides a color Graphic User Interface.