Recent content by Bruce Tomlin

A 7805-based power supply was one of my first Radio Shack projects as a kid back in '77 or so. My parents were worried about something that could (gasp) connect to mains power, but I managed to convince them. Anyhow, I still have it, and just the other day found that I still have the info sheet...

I did okay back in the day (1985). I only had the "phone book" Inside Macintosh, and used that and a copy of MS-BASIC to make my own BASIC compiler. An important step was a program to grovel around the MFS floppy disk directory sectors and swap the data and resource forks of a file, so that I...

For modern purposes, there are plenty of single mechanical keys for sale, and key cap sets for them. All that is needed is more blank PCBs with key footprints so you can wire up your own matrix. The most annoying thing is the +.05" in the pin spacing dimensions, so no chance of just dropping...

From its behavior in the video, it looks more like they use RAM for the custom characters, because when it scrolled, the custom characters got wiped. So probably a character set in the microprocessor ROM to display ASCII, then it's sent to the LEDs as pixels, then some commands to change the...

I can believe it. The newer code just looks more well thought out. It also tries to keep a number entirely in B,C,D,E whenever possible, so that's a big speed-up right there. This was definitely a case where starting over was a good idea. This old code also loves to use the stack, which has to...

Yep, and I verified the block structure by reading the loader code. (there's a commented disassembly in my uploaded zip) Your listing tosses the first data byte of each block and includes the checksum byte at the end as data, so every block is off by one. It misses the F3 (DI) at address zero of...

You got the block structure wrong, it's "3C len lo hi (data) ckhsum". You had the checksum byte before the data rather than after it. It was simple enough that I just hand-edited a hex dump to extract the binary. And of course the loader is in reverse order in the tape, to make the boot loader...

I've cleaned up my old code that added commands to Level II BASIC. It seems that making it work right was messier that it should have been, because IF could go back to the old inner loop if it ended in a statement instead of a line number. This isn't quite cleaned up to the quality of an...

In this case (TRS-80 Level II), CRUNCH did check for lowercase. But it was unbounded on the high end, so it looks "{" should match "[", which is the up-arrow. Applesoft (like most 6502 BASICs) did not. It looks like TRS CoCo also did not.

I did some of this way back in the day and found my code again a couple of years ago. I'll go look it up. The fundamentals are that you have to replace the inner interpreter loop because it isn't sufficiently patchable for adding new commands. You use the patch points that are there to hijack...

Actually the 75188 and 75189 are just TI's part number for the 1488 and 1489. The first hit I found for "75188 pdf" on Google was a data sheet for "MC1488, SN55188, SN75188 QUADRUPLE LINE DRIVERS". The need for +/- 12 volts was the reason that MAX232 exists. Anyhow, one of the coolest things...

I still want to know how much Vtech paid, and to whom... if anything at all. They reused the TRS-80 ROM directly, wiping over the sections they didn't need to add their own custom stuff, but most of it is still the same bytes at the same addresses. I don't know exactly when they were using it...

actually it used shift-up-arrow (or was it shift-down-arrow?) as a ctrl key

FWIW, the difference between "SET" and "EQU" is that SET is only temporary, but it is an error to try to change an EQU value. (depending on your specific assembler, of course)

The original source code that it was derived from could be built with options such as being made for ROM, but those get lost when it's built. It's only relocatable when you find all the places that need relocation and then reassemble it. There was at least one obscure relocation that I needed to...