Jonathan A. Titus

Microcomputer Pioneer

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Hobbyists have been an integral part of the electronics world, and every so often one hobbyist develops an invention that makes an impact within industry. In Jonathan A. Titus' case, he was a computing hobbyist who had the desire to build his own computer. At the time Titus decided to design this computer, the smallest computers were Digital Equipment Corporation's (DEC) PDP-8 series of machines, which took up the space of about two microwave ovens. Titus successfully built his own computer, the Mark-8, in 1973, based on an Intel 8008 microprocessor. The Mark-8 may not have been the first home-built computer that worked, but it was the first to offer a kit design explained in detail in a national magazine. The Mark-8 kit let other hobbyists follow in Titus's footsteps.

Jonathan A. Titus obtained his formal education in chemistry at the following institutions: BS from Worcester Polytechnic Institute (1967), MS from Rensselaer Polytechnic Institute (1969), and PhD from Virginia Tech (1978). In the early to mid-1970's, while Titus worked on his doctorate in chemistry at Virginia Polytechnic Institute and State University, he frequently used minicomputers, particularly a DEC PDP-8/L. As he spent time on these computers he became adept at creating assembly-language programs. But Jon longed for a computer of his own. At the time, minicomputers from DEC and other computer manufacturers cost at least $6,000, which exceeded most hobbyists' budgets. The circuitry and the standard minicomputer core memory modules proved too complex for hobbyists to readily duplicate at reasonable cost.

Early in 1973, Titus requested samples of 8008 chips from Intel, which supplied three devices that would have cost $125 each. Because Titus had no way to read or write PROM (programmable read-only memory) chips, he designed and built a front panel which used switch controls and indicators. The switches served to set individual bits, and by manipulating the switch array, he could load small programs into his Mark-8. Then he could use a keyboard and a display device to enter and examine more program code and data, and test his software.

Titus’ first attempt at a prototype design worked. The computer featured three banks of 256-byte memory. While applying decals to the system, Titus realized that the system needed a name, and since the computer relied on Intel’s 8-bit processor, he named it the Mark-8.

Titus pitched a hands-on construction article for the Mark-8 to Popular Electronics magazine and Radio-Electronics magazine. Only Radio-Electronics responded. The chief editor liked the project and agreed to publish an article about the Mark-8, including circuit board layouts and assembly instructions. A supplemental instruction book advertised in the magazine sold several thousand copies.

"Experimenters realized they could have their own computer, and in fact, such a computer was simple, relatively inexpensive, and easy to build and use," says Titus. "Although few if any 'application' programs existed in 1974, the Mark-8 gave people a way to learn about computers first hand. It blazed a trail for others to follow."

Although not a direct descendent of the Mark-8, Jon with Dr. Chris Titus and David G. Larsen designed several other pieces of computer equipment. In 1977, the Dyna-Micro computer was designed, also featured in a Radio-Electronics cover story “Build Dyna-Micro: An 8080 Microcomputer” (Vol. 47, No. 6, pp. 41-44 & 84). This computer used an Intel 8080 chip and it had a small keyboard for entry of octal op codes. Three output ports provided connection pins for experiments as well as eight LEDs each. During data entry, 16 LEDs indicated an address and 8 LEDs showed the data entered into that location. So, entering a small program using the on-board Keyboard Executive (KEX) firmware was easy for students. This design was licensed to E&L Instruments, which renamed the computer the MMD-1 or Mini Micro Designer. The computer provided 512 bytes of EPROM (256 bytes for KEX and 256 bytes available on a user-accessible socket). The computer included 256 bytes of SRAM, expandable on board to 512 bytes. Eventually, a few interfaces were added: an add-on board that increased EPROM and SRAM space, two UART serial interfaces and an audio-cassette interface for data storage.

The solderless breadboard on the MMD-1 gave experimenters access to bus and control signals. Jon still has a couple of the MMD-1 computers and uses them to test simple devices under computer control, when he doesn't have time to set up a small development system and relearn its IDE for assembly-language or C programming.

Using royalties earned for sales of the Mark-8 designs, Jon bought an IBM Selectric typewriter and became a prolific writer. He has written extensively on computer-related subjects for a variety of magazines, including a series on microcomputer interfacing for Computer Design, Radio-Electronics, and American Laboratory, in the 1970’s, for EDN, in the 1980’s, for the Test & Measurement World, where he became the editor-in-chief, in the 1990’s, and for Design News and ECN (Electronic Component News), in the 2000’s. Now semi-retired, he still publishes in the latter three magazines. Together with David G. Larsen, Peter Rony, and Christopher Titus, he co-authored over a dozen popular books on microcomputers, published by Howard W. Sams in the Blacksburg Continuing Education Series.

For his contribution to computing with Mark-8 design, Dr. Titus was honored in 2002 by the The George R. Stibitz Computer & Communications Pioneer Award.
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His original design of Mark-8 is featured in the computers section at the Smithsonian.
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