Video Card - HP 9000 Series 310 Service Information Manual

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Figure 3-15. HP 98546A Display Compatibility Interface (Video) Block Diagram
Video Card
Input Video
Bit-Mapped video frOln video circuits is input to the video card through the BNC connector
labeled Video In. Depending on the mode of the computer this will be either alpha or graphics
video. In graphics mode, video is sent to the graphics card through a ribbon cable connecting
the two cards. In alpha mode, video and sync pulses are fed to the alpha video circuits.
Tinling 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.
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 programrning. 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 rnonitor'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
Rornan 8 style of characters. Labeling on the printed circuit board next to the switch with a 0
and 1 identifies the respective switch positions.
Functional Description 67