As my digital circuit experiments grew to nearly unmanageable complexity for my skill level in early `92, my electronics teacher, Mr. Kvartek, finally suggested the idea of learning about microprocessors. I specifically remember him describing their use and capabilities as "mind boggling." He soon showed me several shelves of microporcessor trainers, peripheral equipment and training material, hidden away in the supply room. At the time EHS still had a well equipped inventory of digital and microprocessor trainers acquired during the mid to late 80's. Among these were three Fox MT-80Z (Zilog Z80) trainers, and one Motorola 6502 based trainer. They were barely used and gathering dust.
E&L Instruments: Fox MT-80Z
After an unproductive summer, spent playing video games and blowing things up, I signed up for a Lab Assistant credit in Electronics Technology at EHS. For nearly two hours a day, I had all the resources of a well equipped lab at my disposal, and I made good use of them, tinkering further with digital circuits and delving a bit more into the MT-80Z training exercises. Among an assortment of books and other items lost in the clutter of his office, Mr. Kvartek found "The 8085A Cookbook," by Christopher Titus, and let me borrow it. Unlike the MT-80Z training manuals, "The 8085A Cookbook" began with a well written, straightforward description of what a microprocessor is, how it works, both inside and out, and how it is interfaced to the outside world. This is the book that brought it all together for me. Everything suddenly clicked, and I finally understood microprocessors. My mind was racing and snowballing with ideas, picturing and grasping these new found implications and applications.
As luck would have it, the Intel 8085A shared many similarities with the Zilog Z-80. Their architecture and instruction set were mostly identical, so much of what I learned about the 8085A was directly interchangeable with the Z-80. I soon began to develop my own software with machine code, mostly finding creative ways of manipulating onbaord I/O devices on the MT-80Z, such as LED's, DIP switches and a small speaker. As my curiosity grew, I finally began to build, interface, and drive my own circuits with even more elaborate assembler code.
At one point I even designed an 8-bit serializer, using the MT-80Z to input 8-bit patterns into a 74LS151 multiplexer, and scan them into the TTL blanking input of a Tektronix oscilloscope with some assembler code I put together. With the oscilloscope set to X-Y mode, I used two sawtooth signal generators to generate horizontal and vertical sweep for the beam. After carefully tweaking the frequency of these sawtooth signals, I was able to input bit patterns using the DIP switches on the MT-80Z an display vertical bars on the oscilloscope, corresponding to the DIP switch positions. The idea behind this was to develop the capability to eventually manipulate these patterns down to a pixel level and using D/A converters to generate precise H/V sweep, allowing me to use an oscilloscope CRT as a graphical display. Unfortunately, the oscilloscopes we used at EHS did not have CRT's capable of generating a bright enough beam to make this a practical project, and being somewhat leary of toying around with old CRTs scrapped from portable computers, I soon turned my interest to graphical LCDs.
After high school, I began working mainly with the Intel 8085A, designing projects around an OTS development board. This is covered in more detail under my Intel 8085A Peripheral Development System page. In junior college, I tinkered with some 8086 assembler code for a microprocessors course, but never applied it beyond a PC based emulator. At UWF, I stepped into the world of microcontrollers, learning the Motorola 68HC12. This consisted mainly of writing assembler and C programs for the Wytec Minidragon development board. I soon acquired my own Dragon 12 development board for the HC12, and plan to shift my focus towards this platform for future projects.