As I said in the
Fulcrum History
section, Fulcrum sold IMSAI boards -- amongst which was the
IMSAI VIO video board.
However that board was a simple memory mapped video board which suffered
from screen glitches as the screen was being updated. Fulcrum set
about making their own non-memory mapped video board which is described
here.
The "VIO-X" Video I/O Interface as they called it, provided features equal
to most intelligent terminals of the time both efficiently and economically.
It allows the use of standard keyboards and CRT monitors in conjunction with
existing hardware and software. It will operate with no additional overhead
in S-100 systems regardless of processor or system
speed.
Through the use of an Intel 8275 CRT controller with an onboard 8085
processor and 4K of memory, the VIO-X interface operates independently of
the host system and communicates via two ports, thus eliminating the need
for host memory space. The screen display rate was effectively 80,000
baud.
There were two variations of the board.
The
VIO-X1 provided an 80
character by 25 line format (24 lines plus status line) using a 5x7
character set in a 7x10 dot matrix to display the full upper and lower case
ASCII alphanumeric 96 printable character set (including true descenders)
with 32 special characters for escape and control characters. An optional
2732 character generator was available which allowed an alternate 7x10
contiguous graphics character set.
The
VIO-X2 also offered an 80
character by 25 line format but uses a 7x7 character set in a 9x10 dot
matrix allowing high-resolution characters to be used. This model also
included expanded firmware for block mode editing and light pen location.
Contiguous graphics characters however were
not
supported.
Both models support a full set of control characters and escape sequences,
including controls for video attributes, cursor location and positioning,
cursor toggle, and scroll speed. An onboard Real Time Clock (RTC) was
displayed in the status line and could be read or set from the host system.
A checksum test was performed on power-up on the firmware EPROM.
Video attributes provided by the 8275 in the VIO-X included:
FLASH CHARACTER
INVERSE CHARACTER
UNDERLINE CHARACTER or
ALT. CHARACTER SET
DIM CHARACTER
The above functions could be toggled together or separately. This was
an excellent board. Comparables would for example be the
SD
Systems 8024, but none had the useful RTC option on the status line.
