SD SYSTEMS - VDB 8024 Video Display Board
one of SD Systems most successful products. This video board
gave a rock solid 24 line X 80 characters per line B/W display. Its onboard Z80
made screen update instantaneous. It takes a parallel ASCII type keyboard for input.
The VDB utilizes a Z80 microprocessor to perform the control
functions of a video terminal. These functions include LF, CR, full cursor
control, home, clear, scroll and back space. In addition to the basic function
several special additional features are provided. One of these features provides
for specified fields of characters to be enhanced. This field can be enhanced
in any of the following ways: Underline, Reverse, Blink, Protect or combinations.
Another feature of this board is the programmable character generator- This
is a 7 x 8 dot character matrix with 2 bits of descenders to provide upper and lower
case characters in a 7 x 10 dot field. 128 characters are typically available
while 256 characters can be made available using a 2K x 8 PROM. These characters
are displayed in a field of 80 characters in length and 24 lines per page.
The VDB processor runs only during H & V sync to eliminate any disturbance of the
display due to the processor running during the raster scan. There are several
software controllable functions. These include a speed control similar to
a baud rate control and also a scroll up or scroll down. In addition, a set
of 32 special characters are available.
The VDB hardware performs all control and timing functions
as well as the special enhancement functions.
The on board CRT 5027 video timer and controller is used to
perform character count, character line count and row count. The outputs of
these counters are then fed into the RAM or Character Generator (CGEN) to provide
the proper scanning and display of each character in its proper place. This
chip also provides for proper cursor control, horizontal sync, vertical sync and
The Z80 executes the software which controls all functions
of the system. This includes inputting data, storing data in memory, initializing
the CRT 5027, controlling the special functions, cursor control and scrolling.
The manual can be obtained
Other SD Systems S-100 Boards
VersaFloppy I & II
I/O8 Serial Board
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