HP 330 Service Information Manual page 109

Video Boards
Introduction
Video boards allow the computer to send bit-mapped display information to medium or high
resolution monitors. The user may upgrade his computer system from medium to high resolution
by installing a different board. Upgrading is accomplished through an exchange program. It
may be performed by the user with common tools without CE support.
One monochromatic and two color video boards are available for the HP Series 300 computer
systems. The color boards provide four-plane color display capability allowing the user to display
16 colors from a palette of over 16 million colors. A description of these boards follows:
• HP 98542A Medium-Resolution Monochromatic Video Board. This version displays 512
by 400 pixels and drives the low resolution monochromatic monitors.
• HP 9854:3A Medium-Resolution Color Video Board. This version displays 512 by 400
pixel pairs and drives the low-resolution color monitors.
• HP 98544B High-Resolution Monochromatic Video Board. This version displays 1024 by
768 individual pixels and drives the high-resolution color monitors.
• HP 98547A High-Resolution Color Video Output Board. This version displays 1024 by
768 individual pixels and drives the high-resolution color monitors.
These boards make extensive use of large scale integrated (LSI) circuits. Up to six (depending
on the board) NMOS III Display Controller chips provide an integrated bit mapped display with
window-nlove hardware and frame buffer support. Color mapping is entirely handled by another
NMOS III chip called the Frame Buffer Controller. This chip performs color mapping and D to
A conversion. Video memory consists of uses nibble-wide (4-bit) Display RAM (DRAM). The
major difference between these assemblies is the amount of DRAM each has.
Video boards perforrn the similar functions, which are:
• Establish display clock frequency in the computer system.
• Initialize according to the specific monitor used.
• Identifies itself and set character shape by ID /FONT ROM.
• Respond to interrupts on DIO/DIO-II bus to change color map data.
• Control the display RAM maps.
• Color boards output Red-Green/Sync-Blue Video to the color monitor.
• Monochromatic boards output Video/Sync to the monochromatic monitor.
Each of these is explained in the following functional description. Refer to Figure 3-21.
Functional Description
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