Radio Shack CCR-81 Operation Manual

Computer Graphics Operation Manual
----------TRS-BO ® ----------
5/ programming the Graphics Board
The Graphics Board provides 64~ X 24~ byte addressable
pixels on a TRS-8~ Model III. The Graphics Board contains
32K of screen RAM to store video data consisting of four
64K RAMs which are double accessed for 8 bytes of data.
Regular alphanumeric data is stored in the static RAM on
the Video Board. The Graphics Board uses separate hardware
to generate a 64~ X 24~ display, so only one screen may be
displayed at a time. If the video is switched from Text to
Graphics Screen very rapidly, the Video display may lose
horizontal/vertical synchronization.
I/O port mapping is used to read and write data to the
board. The Board is addressable at 8~-83 Hex.
There are four internal registers which can be written to
or read on the board. They are as follows:
1. X-Position
2. Y-Position
3. Data
4. Options
X-address (~ to 127) for data write
only. (~ to 79 for display.)
Y-address (~ to 255) for data write
only. (~ to 238 for display.)
Graphics data in "byte" form. Each
byte turns on or off 8 consecutive
horizontal dots.
8 flags which turn on or off the user
programmable options (Write only).
The I/O port mapping of the board is:
x~ - X-Register Write. (8~)
xl - Y-Register write. (81)
x2 - Video data read or write. (82)
x3 - Options write. (83)
where x denotes the upper nibble of the I/O boundary as
set by-the DIP switches. They are set by the factory at
8~H.
The Graphics Board uses X-Y addressing to locate the start
of a Graphics data byte. The upper-left of the screen is
(~,~) while the lower-right is (~79,239). If the bit is a
1, the dot will be ON. For example, if you wanted to turn
----------lIadlelllaell----------
-114-

Radio Shack CCR-81 Specifications

General

Brand	Radio Shack
Model	CCR-81
Category	Desktop
Language	English