Character Set - NCR PC4I Technical Reference

THE SCREEN DISPLAY
An additional character set is available for reading
under software control, as used by the low resolution
graphics mode of display in GW-BASIC. Essentially
this consists of the same characters as available in
the character set already described. The main
difference is that pixel patterns for the characters
in this set are in a 7 x 7 format (except for
downward tails) contained in an 8 x 8 area.
The pixel patterns for the lower part of this
character set (that is, characters with codes O -
7FH) can be read starting at address OFA6EH, offset
to the beginning of the ROM at paragraph address
OFOOOH: the pixel pattern for the character with code
0 is stored in the first 8 bytes, the pattern for
code 1 in the next 8 bytes, and so on. The last
character pattern (for code 07FH) is stored between
offset OFE66H and OFE6DH.
The procedure for accessing the higher part of this
Alternative Character Set is the sames as for the 16
( x 8 character set, except that
(
• You may specify either low/medium or high
resolution in response to the GRAFTABL menu.
• The pixel pattern for any character occupies only
8 bytes of memory.
• The beginning of the character table is at a
positive offset of one byte to the location
pointed to by the interrupt vector.
This character set is not implemented in the hardware
character generator.
Figure 7.3 illustrates the pixel patterns of the
8 x
8
character set.
7-15