HP 330 Service Information Manual page 129

Display Compatibility Interface
Introduction
An HP 98546A Display Compatibility Interface enables bit-mapped video from the computer to
be compatible with the HP 35721, HP 35731, and HP 35741 monitors when one of the following
operating systems is used:
• HP Series 200 BASIC 2.0, 2.1, and 3.0.
• HP Series 200 Pascal 2.0, 2.1 and 3.0.
Two DIO cards are used and each may be individually replaced. These iterns are included in
the package:
• Video Card.
• Graphics Card.
• Various video cables
Both cards are installed in adjacent DIO card slots. The video card must be in a DIO interface
slot with the graphics card in the accessory slot directly above the video card.
This two-card set has the following functions:
• Bit-Mapped Video Input
• Katakana or Roman 8 Character font.
• 50 or 60 Hz Refresh Rate Selection
• Alpha and/or Graphics Video Output
Figures 3-31 and 3-33 are block diagrams of the cards. Refer to these diagrams for functional
descriptions.
Video Card
Input Video
Bit-Mapped video from a video board is input to the video card through the BNC connector
labeled Video In. The card contains a relay that selects either the externally supplied video
signal (from another video board) or the on-board generated alpha/graphics video to be sent
to the monitor.
Timing and Drivers
Timing clock signals and video driver circuits required to interface the graphics card are on the
video card. Vertical sync circuits are controlled by the position of the 50/60 Hz monitor refresh
rate switch. Both vertical and horizontal sync pulses are output to the video circuits to be part
of the composite video output.
Functional Description
113