Characters; Character Ram; Character Rom/Eprom - Motorola MC68HC05T16 Technical Data Manual

• Interrupt on the leading edge of vertical flyback signal
Character Features
• 128-character ROM/EPROM plus 16-character RAM. Character RAM is dual ported
• Character attribute is on per character basis
• Individually controllable character background
• Character blinking with four blinking rates
9.3

Characters

Characters are stored in a 128-character ROM and a 16-character RAM. The 128 pairs of
character registers are equally allocated for the 4 row buffers, each have 32 pairs. Each pair of
character registers consists of the Character Code register and the Character Attribute register.
The Character Code register selects the particular character from the character
ROM/EPROM/RAM. The Character Attribute register selects the color, background, and blinking
features for that selected character.
9.3.1

Character RAM

OSD character RAM is a dual ported RAM, consisting of 16x(16x16)/8=512 bytes of RAM;
located from $0400 to $05FF. Upon reset, the content of character RAM is random. Every entry
of this 16-entry character RAM occupies 32 consecutive memory bytes, always starting at even
addresses. Users can read and write any byte at any time. OSD can only read the character RAM.
Figure 9-1 shows the memory map of one entry of the 16-entry OSD character RAM.
If 12x16 character dot matrix is selected, bit 3 to bit 0 of all low order bytes at the right-hand side
of Figure 9-1 will not be used for display.
9.3.2

Character ROM/EPROM

The memory arrangement of OSD character ROM/EPROM is the same as that of character RAM.
Character ROM/EPROM is not readable to the CPU in user mode. OSD character ROM is located
from $8000 to $8FFF. Three characters in the Character ROM are fixed, and cannot be changed.
They are shown in Figure 9-2.
MC68HC05T16 ON-SCREEN DISPLAY
9
TPG
MOTOROLA
9-3