In 1984, I was working at Hayes Microcomputer Products. They were the premiere modem manufacturer for small computers, back in the days when modems over telephone lines were a primary means of computer to computer and user to computer communications.
In my job, I created communications software to talk to the modems. The software dialed the modem, established connection, provided terminal emulation (my specialty), allowed for the capture of the data stream to files, printing, file transfer with the remote computer (using protocols like XMODEM and YMODEM), and other features.
These were the early days of personal computing. IBM introduced the PC in 1981, and it had rapidly evolved into a defacto standard computer, shoving out various CP/M designs from the previous decade. Personal computers were so new, people were trying to figure out what to do with them. Word processing, spreadsheets and other office applications had just been introduced.
Hayes was trying to stay at the forefront. We had a laboratory filled with pretty much one of every personal computer, and when new ones came out, we would buy one. In late 1983, we got an Apple Lisa. It was a very different kind of computing experience. It was a curiosity to us, and as there was no programming environment available, we didn't see how we could build software to talk to a modem. Plus, at the price point, there were few buyers.
The Macintosh
Though the Macintosh was introduced in January of 1984, I didn't get hands on one until the late spring of 1984. Yes, we brought one into the lab, and it immediately garnered a lot of attention.
While there were similarities to the Apple Lisa, the small screen with square pixels just seemed sharper and more distinct. The whole interface was friendly and approachable. We messed with MacWrite, MacPaint, and MacDraw. We printed on an ImageWriter, making appreciably decent images unlike anything we could do on another type of computer. There were several of us hooked and enthusiastic.
It's hard to describe those days. At this point, everyone has had decades to become familiar with computers that use a graphical user interface and a mouse or other pointing device to interact. Back then, it was a revelation. It was much more approachable than the command-line interfaces of the day.
As I described it to someone in the early 90s -- other computer interfaces required one to reach toward the computer. You had to learn the special language and commands of that computer. The Macintosh was the first computer that reached back toward you -- the user.
The Machine
The Macintosh was based on a 16-bit Motorola MC68000 processor, running at 8 MHz. This was more than competitive with the Intel-based IBM clones circulating at the time. This processor was a great choices by Apple. It had many registers and powerful instructions for manipulating the bit-mapped screen.
Biggest constraint was memory. The 128 KB in the Macintosh was shared with 24 KB used for the screen, several more KB for operating system usage, leaving about 90 KB to run your program. Most of the critical operating system routines were in the Macintosh ROMs, which saved space. Building a program of any sophistication was difficult -- It was very tight to work with.
The single 400 KB floppy disk drive was also a limitation. Trying to save a file to another diskette could produce an endless amount of swapping. It was the lack of addition storage that kept me from buying a Mac until the Mac SE/20 was introduced in 1987.
Next Steps
By summer, Hayes hired some consultants to look into the feasibility of developing communications software for the Macintosh. In just a few weeks, they had some rudimentary software going and concluded that it was quite feasible.
We were soon green lighted to create a product for the Macintosh.
When I first got into radio, in 1971, I barely knew what I was doing. I had done some shortwave DXing with my GR-81, but that rig worked much better on the AM broadcast band than anywhere else. Just before labor day of 1971, I put up my first outdoor antenna.
Previously, I had just used a spool of magnet wire strung around the ceiling of my attic bedroom. This was not a very good antenna. Just before school started in 1971, I bought a 25 foot roll of small speaker wire and unzipped it all. Soldering the two pieces together, this gave me 50 feet of antenna wire, which I strung out the window, across the garage and into a tree at the edge of the yard.
I was eager to try this new antenna, so I proceeded to tune across the AM broadcast band that evening, and log each station I could. I started about 9 PM, and kept tuning until midnight. The next evening, I continued the process.
Sep 3 log page.
That first night, I had started at the bottom of the band at worked my way upwards. The second evening, I continued upwards, but then reversed and went lower in frequency. This made more sense to me, and my later "countdowns" that I would make in subsequent years all started at the top of the broadcast band and continued toward the bottom.
Sep 4 log page.
This event inspired me that for the next several years, I would try to do a "countdown" around Labor Day weekend. It marked the end of the summer, but also the beginning of the radio season.
I remember it distinctly. I would sit patiently and wait for the AM stations to ID, generally at the top or bottom of the hour. If I got lucky, they would ID sooner.
Hard to believe that event was over fifty years ago.
The 1.0 MHz clock board, attached to the back of the MP-A CPU board.
When I ordered my SWPTc 6800 Computer System, I was expecting a 1 MHz 6800 computer. It wasn't quite.
Yes, 1 MHz seems glacially slow by today's standards, but this was 1977! And the Motorola and MOS Technology chips of that time could access memory in a single clock cycle, so they were just as fast as the Intel or Zilog chips at twice the clock speed. (Those devices needed two clock cycles, minimum, to access memory and typically ran 2-5 MHz)
Perhaps as a cost-saving measure, the SWTPc MP-A board only has one crystal. This crystal connects to the MC14411 bit rate generator, which requires one specific frequency: 1.8432 MHz. The MC14411 contains a number of divisor networks to offer common bit rates for serial communication.
The designers of the MP-A used one of those outputs to drive the MC6800 at exactly 0.9216 MHz through clock conditioning circuitry. The MC6800 has two clock inputs that must be non-overlapping. This required about three integrated circuits and about 20 discrete components to produce. (Motorola later developed the MC6875 chip for this purpose. The later MC6802 had an on-chip clock oscillator and driver)
Clever, perhaps, but disappointing. It meant that my computer was almost 8% slower than specified.
Harsh Reality
Original crystal from my MP-A.
All this assumes you are start with a 1.8432 MHz crystal. In my unit, the crystal was actually 1.7971 MHz! This must have been another cost-saving measure. Perhaps the 1.8432 crystals weren't available, or perhaps they were more costly, since they substituted a unit that was 2.5% slower.
This meant that I didn't have a 0.921 MHz computer, I had a 0.89 MHz computer. It was 11% slower than 1 MHz.
This would not do.
First Modification
Changing the clock speed is actually a simple matter - one need only introduce a clock signal into the conditioning circuits that drive the MC6800. All you needed was a crystal oscillator and a 1 MHz crystal.
Close-up of the clock board.
I used a very simple circuit using two gates of a 7400 to create a very reliable oscillator. Even though this circuit was really simple, I wanted it to neatly attach to the CPU board. So, I etched a small circuit board. This was perhaps my second or third attempt at making a printed-circuit board, so it isn't pretty.
I masked the board by hand-painting etch resist. The lines are not very straight, and the lands have all different sizes. Most of the board was unetched and forms a ground plane that the crystal case is tied to. The result is very crude and rough.
Crude but functional etching.
The smallest drill bit I had was quite large for the pins, so the chips and other components don't rest very snugly, and are held in with solder blobs. All of the parts came used out of my electronics junk box, so they are different sizes. Only three wires connect to the MP-A: 5 volt power, ground, and the oscillator output.
It worked!
I now had a computer which was 11% faster than stock. At the time, It really felt like I had improved the computer.
Overclocking
Having an external clock oscillator means you can experiment with different clock speeds. Some time circa 1980, it dawned on me that I might push the processor faster than 1 MHz
Now, the Motorola 6800 microprocessor line had different codes for different speeds. No letter indicated 1 MHz, and "A" indicated 1.5 MHz, and "B" was 2 MHz (eg an MC68A00 is 1.5 MHz, and MC68B00 is 2 MHz). This wasn't just for the processor, but it applied to all the peripheral devices in the line (MC6810, MC6820, MC6830, MC6850, etc). All of my components were 1 MHz only. Could it possibly work at higher speeds?
At an electronics shop, I found a surplus 2.01 MHz crystal cheap, so I figured I'd give it a try. I removed the 1.0 MHz crystal and installed the new unit.
It worked!
I ran that computer for a couple of years in that configuration, and I never had a problem. Those 1 MHz components could work at 2 MHz, although likely not through the entire 0 to 70 degrees C rating for commercial devices.
This experience proved useful several years later at work, circa 1985. We had upgraded from the 4.77 MHz IBM PCs to 6 MHz IBM ATs. Of course, I opened up mine immediately and noted that the CPU crystal was 12 MHz and socketed. A trip down to the electronic surplus store netted several crystals at 16, 18 and 20 MHz. That IBM AT on my desk would not boot up at 10 MHz (using the 20 MHz crystal), but it ran just fine at 9 MHz. I made the same modification to several other colleague's computers as well to 8 or 9 MHz. We ran that way for years. And when it came time to turn them in, the original 12 MHz crystal was easily swapped back in.
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