HP 330 Service Information Manual page 132

Alpha Video
Alpha video is stored in on-board RAM and provides 25 lines of text with 80 characters per
line. Provisions for inverse video and half-bright user-definable key labels in the bottom two
display lines are enabled through software programming. Text is 8-bit ASCII modified for the
monitors supported. A switch determines whether Katakana or Roman 8 character font will be
used.
Configuration Switches
Two switches determine display refresh rate and alpha character font. Refresh rate is determined
by the switch farthest from the edge connectors and should be set to the line voltage frequency.
Otherwise, the monitor's display may flicker. A 50 Hz and 60 Hz position is available and the
printed circuit board is labeled accordingly next to this switch.
The switch nearest the edge connectors determines the character font. When the computer
system is used in Japan, or when BASIC or Pascal operating systems with revisions lower than
3.0 is used, this switch should be placed in the 0 position to enable the Katakana characters to
be displayed. For all other countries, the switch should be placed in the 1 position to enable
the Roman 8 style of characters. Labeling on the printed circuit board next to the switch with
a 0 and 1 identifies the respective switch positions.
Video Output
Alpha and/or graphics Video is combined with sync pulses from the tilning circuits as a com-
posite video signal. Video is output from the Monitor BNC connector on the video card's rear
panel.
When graphics mode is selected by software, graphics video from the graphics card is input·
to the video card and output from the BNC connector labeled Monitor. When alpha video is
selected, alpha video is output from the same connector. This type of video is called separate
alpha/ graphics video.
For systems using a color monitor with this card set, the green video with sync is input from
the color video circuits in the computer and is processed the same as composite monochrOlne
video. The Monitor output, which in this case is green video with sync, is connected to the
green input connector on the color monitor. Red and Blue outputs from the video board in the
system slot are fed directly to the Red and Blue input connectors on the color monitor.
Graphics Card
Circuits required to control the graphics video are on the graphics card. This card is the same
one used with the HP 98204 Composite Video Cards for Series 200 computers.
Graphics Video
Inputs from the video card through the ribbon cable are converted to a 390 by 512 graphics
display and stored in on-board RAM. Graphics memory is organized such that the first 8 pixels
displayed in the upper left-hand corner of the display correspond to the first byte of memory
in graphics RAM. Each succeeding byte corresponds to the next 8 pixels to the right in the
graphics display.
Graphics Video Output
Graphics video is sent back to the video card through the ribbon cable connector.
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Functional Description