Character Rom - Zenith Data Systems Z-100 Series Installation Manual

Page
3.2
General Theory of Operation
The CPU addresses the RAM beginning at location BOOOO. The AO bit
is used to enable either the display RAM or the attribute RAM. This causes
the display to be addressed using even numbers and the attribute RAM
to be addressed with odd numbers. Example addresses are shown in
Table 3.1.
Table 3.1. Character/Attribute Addressing
DISPLAY LOCATION CHARACTER ADDRESS ATTRIBUTE ADDRESS
1 BOOOO BOO01
2 BOO02 BOO03
3 BOO04 BOO05
4 BOO06 BOO07
80 (last in line 1) BOOAO BOOA1
81 (1 st in line 2) BOOA2 BOOA3
1975 (1 st in line 25) BOF5E BOF5F
2000 (last on page) BOFAO BOFA1
Character ROM
The character ROM installed on the card at the factory is an 8K x 8
ROM which provides decoding of the ASCII code stored in the RAM into
pixel on/off instructions. The standard ROM provides decoding for two
256 character fonts. An optional 16K x 8 ROM may be used to provide
up to four fonts. The font in use is software selectable.