Radio Shack TRS-80

I have a TRS-80 that still ran last time I tried. It used audio cassette tapes for storage, but I don't have one, so I built a cable to use a modern voice recorder to read and store data on. I've been wanting to build some kind of project for it that uses the old school nature of the machine with modern conveniences. As an example, it's way easier to create graphics now, but the machine has really limited methods to recreate those.

Oh man you gave me flashbacks. The TRS-80 Model II's OS, TRSDOS-II, had a built-in debugger that was little more than a monitor. You could step through instructions, examine and write to memory, set breakpoints to absolute memory locations, and that was it. I remember hand-assembling tiny Z80 programs in that thing and jumping into them, just to test my understanding of how machine code programs worked and how the computer executed them, and being super thrilled when I could get an A to appear somewhere on the screen or something. The machine had a much more complete assembly language programming toolkit which I also used to write more sophisticated programs, employing this debugger to examine them. But I felt like I'd "cracked the code" of the computer when I plugged hex numbers into RAM and then ran them straight from there. Most CPU ISA documentation should give you the opcodes that correspond to instruction mnemonics. You may have to plug in your own operands (registers, etc.) into bit fields in the instruction encoding. If you're serious about hand-assembling to begin with this should be no problem.

Words cannot even describe how much I loved my TRS-80 pocket computers. As far as having something in your pocket which you can program on, even today there's nothing quite like it. Even touchscreen phones are not a replacement. The TRS-80 pocket computers had actual keyboards, which were small enough to make a portable form-factor, but large enough that you could thumb-touch type on them. Alas, we've gone from being pocket programmers to doom-scrollers.

I gasped when I saw this screen, it was the first game I played on a computer, my science teacher's TRS-80 he brought to school. My friend Jim and I would take turns sitting at the keyboard and calling out commands to type. I haven't seen that screen in over 40 years. Later that year I got my first programming job writing some program in basic to track grades for the teacher. Goodness it brings back a flood of memories, the black science lab table the computer was on, the green or was it amber screen, the floppy disk drive thunk when you closed it and the sounds of the drive working. Our excitement when we would destroy an enemy, or make it safely to a space station. What a great time we had with that simple machine.

The Z80 will always be my first love, in a TRS-80 Model 1 and soon after, the Vector Graphic Vector 3 which was a sturdy S-100 machine running CP/M. Robert Harp of Vector was an extremely competent designer faced with a challenge, a computer with CPU, CRT and keyboard in one unit. All-in-one machines were a challenge because noise from the video stream and HV flyback transformer pervaded the insides, so he restricted the 6 card S-100 cage width to a few inches and found the worst transients on signal lines and placed extra conditioning on the bus, mods reported back to Zilog to assist with future Z80/S-100 builds. The Vector 3 paper manual had 40 dense pages in the back with commented assembly of its entire BIOS. That was a nice touch and I taught myself assembler from it.

I learned to code on a TRS-80 Model 100, in BASIC, when I was 7 years old or so. Nothing Unix-like about it, but as an introduction to programming concepts I got a lot of mileage out of it. The upside is, there are no distractions, and it basically doesn't do anything except let you write text or short BASIC programs. It's essentially a big keyboard with a little chunky LCD display and it runs a long time on AA batteries. I dragged it everywhere with me as a kid, along with the BASIC manual, trying to figure out how to get it to do things. The portability was a big plus, cause I could just keep experimenting whenever I had ideas.

> There's something very human and intimate in the usage of it, despite modern clamshells obviously having better viewing angles and giving you a better posture. They feel very natural and intuitive, in the same way a pen and paper does. There's also something more social about it, if you're using it to take notes while around other people. A screen pointed towards you is a private space; a screen visible to the room is more public (and less prone to distraction as a result because it's obvious to those around you if you're fooling around). I use a TRS-80 Model 100 as a notetaking device for that reason. (Well, also because it's nearly incapable of doing anything that could distract me on the go!)

It has me wishing the TRS-80 Model 100/Dynabook form factor had caught on more. Honestly, yes, I can understand this. A laptop screen pointed towards you feels like a private space, since other people can't easily see it. And indeed, I've definitely gotten work done in meetings for this reason. A device with a screen easily visible to everyone at the table I don't think would have this temptation. I sometimes use a Model 100 when I need to take notes without distractions, actually.

BASIC? GOSUB was so much worse than GOTO in that it had a stack for the current line but no stack for variables so you could not write recursive functions. I think Fibonacci as a recursive function is malpractice but boy was it a hassle to write Quicksort in BASIC although I had no trouble coding up an FFT (1950s FORTRAN style) from first principles in BASIC on TRS-80 Model 100 on a bus ride across Vermont. Funny though I did come to a conclusion that for the Arduino programs I wrote I didn’t need a stack at all.