I'm still working on Sierpinski. Ahl never identified his variables, some of which are readily identified, others are more obscure. At any rate SP (an integer nevertheless converted into its floating point representation in Applesoft), is pretty clearly "stack pointer," which is the index value in array ST (stack, obviously).
What aren't clear are TP and PS, which are changed in the push and pop stack subroutines. When TP=0, we draw three segments, when TP=1, we draw one. When SP is 1, TP is 1; when SP is 2, TP is 0. These seem to determine which of the four 3-part segments we're drawing, right, up, left or down, or the single, 1-part, connecting segments. I'm making progress.
As regards the RETURN WITHOUT GOSUB AT 190 error, I think I should incorporate a POP statement in the pop subroutine when SP and TP are both equal to zero, which seems intended to indicate the curve is closed. That the curve of that particular order is complete. I've never used POP before, so that'll be educational.
But, I'm not exactly sure about that, because I don't have a clear understanding of the flow of control; and so more study is necessary.
But it is becoming less murky.
In other news. as part of my effort to stay away from the news, I haunt a number of forums. I seldom have anything of value to offer, so I mostly just lurk. Sometimes I learn something. Sometimes it can be as frustrating as watching the news. That happens most often a DP Review where some people are needlessly, or obliviously, harsh in criticizing someone's photos. Especially if the OP is extolling the virtues of some lens. There's always someone who has to display their superior knowledge and experience, and do so in a way that seems intended to belittle the OP.
I tend to visit DP Review far less often than in years past, but I'm kind of grasping about for distractions these days.
But I also visit the HP calculator forums, and can be harmlessly distracted for a while. But, it's like cameras used to be for me. I'd read about someone else's gear, and decide I had to have one for myself. Which probably accounts for the ridiculous number of cameras I own.
Anyway, some clever people have reverse engineered the little software cartridges for the TI-95 and TI-74 BASICalc. This was exciting news, as I have two of each. I'm a sucker for modern mods to retro gear. In the course of the thread, I learned that later models of the TI-74 were able to address up to 32K of external (cartridge) RAM. TI sold an 8K RAM cartridge with a (non-replaceable) coin cell inside that could be used as a kind of RAM disk, or to expand the available RAM to the cpu from 8K to 16K.
Those coin cells have long since gone dead, and it wasn't always clear to me whether they would work as volatile RAM with a dead battery. It didn't seem to matter, because even after haunting ebay for months, I'd never seen one come up for sale. Even the program ROM cartridges seemed to command rather absurdly high prices. (All of us old farts with too much money and time on our hands keep driving up the prices, I guess.)
Well, the prospect that there might be a new RAM expansion cartridge coming for the TI-74, that would be larger than the 8K original, prompted me to look and see what was on the market. Both of my TI-74s have relatively low serial numbers, and likely would not be able to see more than 8K of additional RAM.
Anyway, as these things go, or luck would have it, there was a TI-74 with an 8K RAM expansion cartridge for sale! It wasn't an auction, and there was a "make offer" button, so I made an offer. It was listed for $65, which was itself, in my experience, a great price. But together with an 8K RAM cartridge, I could easily see it going for twice that price, or more.
Sometimes, you get lucky. Like I did with the seller who sold me an Apple IIc external disk drive, with a free Apple IIc computer included! And a damn good price for the disk drive. Too bad they didn't pack it better. I'm still looking for a replacement space bar.
Anyway, I offered $59 for it and the offer was immediately accepted. It arrived this afternoon.
Cosmetically, it's in great condition. LCD screen isn't showing signs of degradation. Serial number is astronomical, 9-million something. But the date of manufacture is 7/87, which is only a year later than the 1986 year of manufacture of my other two. (One is 00847, the other is 10k-something. That one has a rotting LCD.)
Batteries were installed, but not leaking. Powered on fine. I have the manuals, so I had to look up how to check to see how much memory was available. It's a ROM routine you have to CALL to turn the cartridge into RAM available to the cpu. CALL ADDMEM, makes the RAM available and turns off the file storage function.
To see if it worked, I entered FRE(0), which reports the amount of RAM available. (FRE(1) would report the amount of RAM consumed by the program in memory.)
Well, success! FRE(0) reports 15902 bytes available. So it would appear that a dead battery doesn't preclude using the RAM for program memory. I'll have to fill a large array to verify it, but it seems reasonable to believe it'll work just fine.
Of course, what the hell need do I have for a nearly forty year old handheld BASIC computer with a single-line LCD display? None. Just something to play with, to pass the time. To recall what "the future" once looked like.
I have a printer for the TI-74, and it can power the computer while you're changing batteries. (I think. It's been a while since I've played with it.) So the idea would be to write a little menu-driven program with a number of little sub-programs to call from the menu. 16K is quite a bit of memory for a little computer. Really, its biggest limitation is the display, but it's intended to be portable.
And I just recalled that I bought a little arduino device someone made that's supposed to allow the 74 to interface with a cassette tape drive. I was planning on trying to use the recorder feature in my iPod.
And someone else on the HP forum is building new HP-IL interface boxes (PIL-boxes), and those are supposed to be available sometime soon. I have a couple of HP-75s and an HP-71b with the HP-IL interface, and the HP-IL video interface.
I don't know what my kids are going to do with all this crap when I die. I'm sure it'd be a pain in the ass to sell it, but they'd probably get a fair amount of money for their trouble. I'll be past worrying about it though.
Originally posted at Nice Marmot 17:44 Wednesday, 23 October 2024