HP 330 Service Information Manual page 114

Identification and Font ROM
Each video board has an ID /FONT ROM. This is a 16 Kbyte wide ROM that supplies the CPU
with information about the video board type. Initialization and dot clock frequency information
is also provided.
Alpha character font is the size and shape of the dot matrix used to create letters, numbers,
and other keyboard symbols. The system monitor will display the font defined in the ID /FONT
ROM during computer power-up and self test. If another font is required for the application, the
operating system or application software can specify another available font to be used. Standard
FONT, or pixel display matrix for the video boards is shown below:
Video Board
Medium-Resolution
High-Resolution
Clocks and Timing
Character
Matrix
9 by 12
6 by 10
Character
Cell
10 by 15
8 by 16
The display clock frequency is different for each video board. At power-up, the CPU executes
instructions from the Boot ROM to determine the presence of and type of the video board.
Data in the ID /FO NT RO M is placed in a Display Controller register to set the display clock
frequency.
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Functional Description