This was the board that launched the
Cromemco company. It was the first home computer color video board and went on
in modified forms over the years to be utilized in specific Cromemco graphic
applications such as weather charts for TV stations. It was a two board set. It
was first described in
Popular Electronics in Feb 1976.
This board set was a marvel at the time
(1977). It was designed by Terry Walker at Cromemco. Using only MOS & 7400 IC's the pair of boards that together
allowed nice color graphics to be displayed on a home TV screen. Up until then,
the only comparable electronics for the hobbyist were ones based on the
circuitry described in detail in the pivotal Don Lancaster book the
The board was a two board set they were
connected by a 16 pin ribbon cable that ran up and over one board and down to
the next board behind it. The boards accessed up to 2K of system RAM via
DMA putting wait states on the CPU while the info from RAM was picked off. This
RAM location could be anywhere on a 1K boundary in the 64K space. Various
resolutions of graphics display were possible ranging from 32X32 color pixels up
to 64X64 displays. Primitive by today's standards, but a marvel at the time. Ports
0FH was hard wired as the control/display format ports. Video output was
generated by board 1. Board 2 was used to communicate with the computer CPU.
Video output was composite video which
could be sent directly to a composite video input of a TV (if you were lucky at
the time to have one with this option) or through the TV antennas via a
small RF converter board. They recommended a converter from ATV Research (see
The Dazzler came about when Roger Melen of Stanford University saw an
article in Popular Electronics magazine, demonstrated the original
After seeing it, he purchased Altair #2 and with his friends Harry Garland
and Terry Walker built an add-on video board for the machine.
The "TV Dazzler" was originally developed as a display device for
the Altair Cyclops version of the Cyclops camera developed by Terry Walker.
The history of the development of the Cyclops cameras and the TV Dazzler
here. This board
set, (the Dazzler), was first introduced at the Homebrew Computer Club on
November 12, 1975.
Like many early S100 board projects of the time, the
Dazzler was originally announced as a self-built kit in Popular
Electronics. Sales were so fruitful that Melen and Garland
formed the company Cromemco to sell the
Dazzler and their other Altair add-ons, selecting a name based on Crothers
Memorial Hall, their residence while attending Stanford.
Cromemco quickly branched out into their own line of Z80-based S-100
compatible computers. Over time these became the company's primary products.
Cromemco also sold a package of simple
games/graphics for the Dazzler boards. These were supplied on paper tape! or cassette
tape or 8" floppy disks (later).
The manual for the board can be obtained
The manual for the computer games that
ran with the board can be obtained
Information about adapting the board to
work with a TV RF signal can be obtained
an early (1976), Popular
Article for the board
The Cromemco SDI Video Board
In 1979 Cromemco replaced the original
Dazzler with the “Super Dazzler”. The Super Dazzler Interface (SDI)
had a 756 x 484 pixel resolution with the capability to display up to 4096
colors. Its onboard two-port memory was used for image storage for higher
performance. Unlike the original Dazzler which had a composite video output
signal, the SDI board used separate RGB component video outputs for higher
resolution. The SDI also had the ability to be synchronized to other video
Interestingly, the Cromemco SDI board became the systems of choice for
television broadcast applications. They were also widely used by the
United States Air Force in Mission Support Systems.
an early Byte
for the board.
The manual for the SDI board can be found
In December 2013, I decided to fire up an old Dazzler
board I had. I placed it in a CompuPro box (see picture below).
This took some effort to get the system working. First, unlike most
later S-100 boards, this early board would only display graphics with the
corresponding Cromemco CPU board the "ZCPU"
board. While the Dazzler would not interfere with other S-100 bus CPU
boards, the image displayed on the screen was always a blank white color.
Furthermore, a number of older S-100 bus RAM cards would not work (display
graphics) with the Dazzler board. Surprisingly this included the
RAM 16 and RAM 21 boards. Fortunately both the Cromemco "ZCPU" and
RAM+PROM N8VEM/S100 Computers worked fine with the board. The
Cromemco ZCPU board requires an external EPROM which was supplied on the
RAM+EPROM board. However the ZCPU board is only capable of addressing
up to 64K of RAM so I had to utilize a non-banked CPM3 system on a CF card
board (with a 44K TPA).
I have not looked into why the Dazzler DMA does not work with a number of other (non
Cromemco) CPU boards. It's not absolute however, I do know the Dazzler
worked with the SD Systems Z80 CPU board
- my original S100 bus CPU board!. Perhaps others could be
added to the list. BTW, it is this type of issue that lead to the
standardization of the S-100 bus signals in the form of the IEEE-696 standard
- used if almost all later S-100 boards.
I actually no longer own a classical CRT TV set. I converted the
Dazzlers Comp. Video output signal to a VGA LCD display utilizing a "converter
box" . A number of these are available these days. I really like the
Atlon (AT-RGB-110) shown in the picture below.
The next challenge was software. Most Dazzler programs were written
before CPM became common and so, as written, are really not compatible, often
residing in RAM at 0H. The most famous Dazzler program was "KScope".
This simple program (less than 200H byte of RAM), delivers a spectacular
display of colors/patterns continuously. I rewrote the
program to load with CPM and run in the above system. Here is a
brief video of the pattern seen:-
The S-100 Bus Dazzler Board in Action:-
The two short (amateur) videos below shows the
KScope graphics action (left) and another Cromemco demo video (below).
To play this video click on the arrow within the
To play this video click on the arrow within the
The KSCOPE program itself can be obtained
Other games software can be found
Other Cromemco 100
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