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ARCHIVE PYTHON DDS-DC OAT DRIVES---PRODUCT DESCRIPTION MANUAL
8.2 Block Diagrams
The electronics of all Python data compression models that use the self-contained Python 3.5-inch DDS-DC
drive (Models 4322, 4542, and 4352) are laid out on one main printed circuit board (PCB) and five small
PCBs. The five small boards control specific functions:
o
The RF PCB controls the head assembl y.
o
The Switch PCB contains the eject switch and the front panel LEOs, and other switches.
o
The SCSI Controller PCB contains the SCSI controller, buffer memory, the AHA3101 data
compression chip, compression memory (SRAM), and ECC processor.
o
The SCSI Interface PCB contains the SCSI connector, power connector, configuration switches,
serial port, tenninator power jumper, and tenninators.
o
The Capstan/Cylinder Drive PCB contains the cylinder servo circuits and the cylinder and capstan
drivers.
Figure 8-1 is a simplified block diagram that applies to all models of the Python DDS-DC drives. Figure
8-2 is a simplified block diagram of the SCSI Controller PCB for Python models 4322NT and 4542NT.
Figure 8-3 is a simplified block diagram of the SCSI Controller PCB for Python models 4322NP, 4542NP,
and 4352XP.
8.3 Python DDS-DC OAT Drives
This section generally describes the hardware design features of the Python data compression drives. You
may want to refer to the block diagrams referenced in Section 8.2 as you read this infonnation.
Python computer OAT drives use the helical scan recording method employing a four-head design. Four
direct-drive motors and one brush-type motor are used in the drive. Also, the read and write functions are
implemented using LSIs. Engineering decisions such as the modular partitioning of the electronics and use
of surface mount, low power commercial and custom LSIs allow Python drives to confonn to the industry
accepted 3.5-inch fonn factor. These design features are also important contributors to the overall reliability,
durability, and perfonnance of the drive.
Additionally, the Python mechanism is designed for minimum tape wear and prevention of damage to the
tape. The modes or operational states, such as stop, rewind, play, etc., are specifically implemented to reduce
mechanism and tape wear. Fewer mechanical mode changes result in less wear on key drive components. In
some cases, the need for a mode change is circumvented using the Pause mode, which stops the tape without
activating the mechanism. Figure 8-4 shows the operational modes in relation to mode changes. All mode
selection is perfonned by the controller finnware. The host computer does not directly control mode
selection.
8-2
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