Cromemco Dazzler

Cromemco's Dazzler (or TV DAZZLER) was a graphics card for S-100 bus computers. Released in 1976,^[1] it is the first commercial graphics card available for microcomputers.^[2] Multiple Dazzler cards could be installed in a single machine and synched together, a feature which could, with minor modification, be used to genlock. Genlocked Dazzler cards drove ColorGraphics Weather Systems displays that generated most of the weather imagery seen on US television in the early 1980s.^[3]

History

The Dazzler came about in a roundabout fashion after Les Solomon, an editor for Popular Electronics magazine, demonstrated the original Altair 8800 to Roger Melen of Stanford University. After seeing it, Melen purchased Altair #2 for his friend Harry Garland to work with. The two built a number of add-ons for the machine, starting with an early video digitizer called the Cyclops and then moving on to the prototype Dazzler.^[1][2] The Dazzler was first introduced at the Homebrew Computer Club.^[2]

Like many early microcomputer projects of the era, the Dazzler was originally announced as a self-built kit in Popular Electronics.^[4] In order to "kick start" construction, they offered kits including a circuit board and the required parts, which the user would then assemble on their own. This led to sales of completely assembled Dazzler systems, which became the only way to purchase the product some time after. Sales were so fruitful that Melen and Garland formed Cromemco to sell the Dazzler and their other Altair add-ons, selecting a name based on Crothers Memorial Hall, their residence while attending Stanford.

When Federico Faggin's new company introduced the Z80, Cromemco branched out into their own line of Z80-based S-100 compatible computers almost immediately. Over time these became the company's primary products. Combinations of their rackmount machines and the Dazzler formed the basis of ColorGraphics Weather Systems (CWS) product line into the late 1980s, and when CWS was purchased by Dynatech in 1987, Dynatech also purchased Cromemco to supply them.^[3]

Over time, Cromemco sold a number of games and basic graphics programs on paper tape and diskette, including Spacewar! in October 1976.^[5]

Description

The Dazzler used over 70 MOS and TTL IC's, which required two cards to hold all the chips,^[6] "Board 1" held the analog circuits, while "Board 2" held the bus interface and digital logic. The two cards were connected together with a 16-conductor ribbon cable. Although the analog card did not talk on the bus, it would normally be plugged into the bus for power connections and physical support within the chassis. The manual also described a way to "piggyback" the two cards with a separate power cable to save a slot. Output from the analog card was composite color, and an RF modulator was available for direct connection to a color TV.

The Dazzler lacked its own frame buffer, accessing the host machine's main memory using a custom DMA controller that provided 1 Mbit/s throughput.^[7] The card read data from the computer at speeds that demanded the use of SRAM memory, as opposed to lower cost DRAMs. Control signals and setup was sent and received using the S-100 bus's input/output "ports", normally mapped to 0E and 0F. 0E contained an 8-bit address pointing to the base of the frame buffer in main memory, while 0F was a bit-mapped control register with various setup information.

The Dazzler supported four graphics modes in total, selected by setting or clearing bits in the control register (0F) that controlled two orthogonal selections. The first selected the size of the frame buffer, either 512 bytes or 2 kB. The other selected normal or "X4" mode, the former using 4-bit nybbles packed 2 to a byte in the frame buffer to produce a 8-color image, or the later which was a higher resolution monochrome mode using 1-bits per pixel, 8 to a byte. Selecting the mode indirectly selected the resolution. In normal mode with a 512 byte buffer there would be 512 bytes × 2 pixels per byte = 1,024 pixels, arranged as a 32 by 32 pixel image. A 2 kB buffer produced a 64 by 64 pixel image, while the highest resolution used a 2 kB buffer in X4 mode to produce a 128 by 128 pixel image.^[8] In normal mode the color was selected from a fixed 8-color palette with an additional bit selecting intensity, while in X4 mode the foreground color was selected by setting three bits in the control register to turn on red, green or blue (or combinations) while a separate bit controlled the intensity.

See also

• MicroAngelo, a higher-resolution system for S-100 computers
• Matrox, Matrox's first graphics product was a video card for S-100 machines, the ALT-256

References

Notes

1. ^ ^{a b} Les Solomon, "Solomon's Memory", in Digital Deli, Workman Publications, 1984, ISBN 0894805916
2. ^ ^{a b c} Harry Garland, "Ten years and counting", Creative Computing, Volume 10, Number 11 (November 1984), pg. 104
3. ^ ^{a b} "WeatherCentral History", boasts that by 1982 70% of the top 50 TV markets in the US used CWS
4. ^ Walker
5. ^ Cromemco Inc., "Spacewar", 1976
6. ^ Manual, pg. 3
7. ^ Manual, pg. 4
8. ^ Manual, pg. 6

Bibliography

• Cromemco Inc., "Dazzler Instruction Manual", November 1978
• Terry Walker, Roger Melen, Harry Garland, Ed Hall, "Build the TV DAZZLER", Popular Electronics, February 1976, pg. 31-40

External links

• Saga of a System - David Ahl's story of how he got his Altair 8800/Dazzler system built, includes some sample images
• Cromemco Dazzler, image of the original design and its instruction manual