The Venerable Old Commodore 64
February 19, 2009 6:50 AM   Subscribe

The Commodore 64 In Pictures. Tom's Hardware, a respected authority on all that is cutting-edge in modern PC components, takes a break from reviewing the latest video cards to bring us a lovely trip down (8-bit) memory lane. If this well-annotated slide show isn't enough to satiate your nostalgic appetite, there's more to remember at rival fansites Lemon 64 and C64.com.

And you might be pleased to note that Press Play On Tape (a previously posted The Commodore 64 Revival Band) can be seen in concert next month. In Copenhagen. (Previously, previously, previously.)
posted by grabbingsand (66 comments total) 14 users marked this as a favorite

 
Bah, you kids and your computers. I can still play Guitar Hero on my C64 just fine, thank you.
posted by mhoye at 6:56 AM on February 19, 2009 [2 favorites]


The 5.25" floppy notcher. It's like getting a second disk FOR FREE.
posted by These Premises Are Alarmed at 6:59 AM on February 19, 2009 [5 favorites]


Screw the C64. The ZX Spectrum rules!
posted by schwa at 7:09 AM on February 19, 2009 [1 favorite]


I remember thinking of my big ugly noisy 1541 as mass storage, but I just read that it was "a single-sided 170 kilobyte drive for 5¼" disks." Jesus. Was it really just 170K per disk? And it was so expensive for what we got: "Priced at under US$400..."
posted by pracowity at 7:12 AM on February 19, 2009 [1 favorite]


C64 too exspensive - VIC20 it was.
posted by stbalbach at 7:19 AM on February 19, 2009 [1 favorite]


The thing I miss most about my C64 is that it was the last computer I ever owned where I knew how it worked. I had complete hardware schematics and complete assembly code source for the OS and I actually knew how it worked.
Ever since, computers have been magic boxes of mystery.
posted by rocket88 at 7:20 AM on February 19, 2009 [5 favorites]


I remember scrimping together a few bucks every couple months for an issue of Ahoy!. I'd spend the next day or two typing in a few thousand lines of hexidecimal codes printed at the back of the issue, just to play a game with the sophistication of Pong. We couldn't afford a disk drive back then, so once I turned the C64 off, all that work was lost, assuming that I didn't mistype some of the hex codes and end up with a broken app. Good times.
posted by Blazecock Pileon at 7:23 AM on February 19, 2009 [1 favorite]


load "*",8,1
posted by Staggering Jack at 7:28 AM on February 19, 2009 [10 favorites]


My wife's business computer was our C64 running Paperclip with a BI-80 card, an amber 80 column monitor, printing to a Brother daisy-wheel printer. Booted up faster and had better output than the IBMs there ...
posted by rfs at 7:34 AM on February 19, 2009


Ah, I still remember when we bought a 1571 disk drive and what an improvement it was over the 1541. Double-sided disks without having to flip them, imagine that! And an optical sensor to detect when the read/write heads were in the home position, instead of repeatedly (and loudly) bashing them against a mechanical stop. And it was faster, too, but only when used with a C128, which was also a fun machine. Nevertheless, the VIC-20 is what I still have in my basement for nostalgic reasons.
posted by FishBike at 7:38 AM on February 19, 2009


I'm glad I went to college, blah blah blah, but really, I'm 100% sure that my last 4 jobs are a lot more directly related to the time I spent as a kid fucking around with my c64.
posted by COBRA! at 7:40 AM on February 19, 2009 [12 favorites]


Ha! Spectrum guys! With you colour clash and inadequate sound chip. C=64 4-EVAH!
posted by Artw at 7:41 AM on February 19, 2009 [4 favorites]


Oh back in the day when only computer nerds could use computers. I never had a C64. My friend did. I remember long load times but the graphics were great! ..... Ok they were terrible but we had better imaginations at the time. I also remember our first IBM dos game we had. It was Captain Comic! That game was awesome......
posted by Mastercheddaar at 7:42 AM on February 19, 2009


C64 too exspensive - VIC20 it was.

It was C16 for me. It looked a lot cooler than the C64!
posted by elmono at 7:50 AM on February 19, 2009


Floppy drives were for posh kids. Rounded brown tape deck all the way!
posted by Artw at 7:50 AM on February 19, 2009 [1 favorite]


I remember how difficult it was to find a 24 pin card edge connector so I could build a reset button.

Ah, the days of warming one's hands on the disk drive.
posted by Foosnark at 7:53 AM on February 19, 2009


Ohh, man. I had an SX-64. It was (23 pounds of) portable, and had a built-in color monitor and a modem!
posted by Floydd at 7:55 AM on February 19, 2009


Ha! Spectrum guys!

Hey, the Spectrum was a *fantastic* computer -- compared to the ZX81.

Compared with everything else on the market .... well, it was cheaper than everything else.

And it's still viable today! You could use one to balance you chequebook, play Hunt the Wumpus or mount it on the dashboard of your C5 and use it to render a psychedelic lightshow that you'd display on your iPhone!

If you give me a peek at it, I'll be happy to poke your ram all night long.
posted by PeterMcDermott at 7:56 AM on February 19, 2009 [1 favorite]


The thing I miss most about my C64 is that it was the last computer I ever owned where I knew how it worked.

That's it exactly: it was complex enough to be magical, but simple enough that you felt you had a chance of fully understanding it.

(But then you saw the things that the demo coders did with it and realized that actually, there was a whole other level of mastery that you would never, ever reach...)
posted by We had a deal, Kyle at 7:58 AM on February 19, 2009 [2 favorites]


Oh goodness, I had so many of these buggers when I was younger... I was buying them and then wearing them out or breaking them well into the early 90s. Pretty much entirely for running Wasteland, too... damn those murderous Boa Tronstrictors in the Vegas sewers!
posted by FatherDagon at 7:59 AM on February 19, 2009 [1 favorite]


Ohh, man. I had an SX-64.

Nice, but not my fetish object of choice. I still can't recall wanting another computer as badly as I wanted one of these. Possibly the GRID Compass, but it was a very close run thing.
posted by PeterMcDermott at 8:05 AM on February 19, 2009


I haven't been near Tom's Hardware since Rob "Dead End" Enderle started submitting articles (Enderle writing for such a site is a bit suspicious and was also the straw the broke the camels back for me). But the promise of nostalgia has lured me back.
posted by Homemade Interossiter at 8:12 AM on February 19, 2009


MetaFilter: POKE 53281,6
posted by Spatch at 8:16 AM on February 19, 2009 [5 favorites]


Spectrum represents! Damn you spoiled, snotty Commie brats with your extra 16K and your superior graphics.

(Although I also had a VIC-20. Quite something: a computer which could run out of memory with just a couple of pages of code...)
posted by Skeptic at 8:22 AM on February 19, 2009 [2 favorites]


COMPUTE!'s Gazette and Speedscript y'all! And of course: GEOS.
posted by ao4047 at 8:26 AM on February 19, 2009 [2 favorites]


<-- Wrote several term papers and book reports using GEOS.
posted by grabbingsand at 8:30 AM on February 19, 2009


God, GEOS blew my mind the first time I saw it. Then I forgot about it for about a decade, and had my mind re-blown when I was using a friend's Mac Classic and suddenly realized that everything looked really familiar.
posted by COBRA! at 8:32 AM on February 19, 2009 [1 favorite]


Did we actually type programs from printed listings in paper magazines? Shit.
posted by pracowity at 8:59 AM on February 19, 2009 [3 favorites]


TRS-80
don't say maybe
I got my rhymes and my programs
on my audio tape, lady!

I got color basic
and you know that I can POKE
I got more goto statements
than the romans got POPE

You know I'm playin Zaxxon
till the end of time
I know the Dungeons of Daggorath
like your mama knows wine

You can say what you want
about your C-64 and your apple IIC
butI got 16K extended basic
and that's enough for me.

posted by freebird at 9:26 AM on February 19, 2009


Another VIC-20 guy over here. Actually, it was called VC-20 ("VolksComputer") in Germany, due to the sexual homonym it otherwise had.

Golden memories are coming into my mind. Before I was able to afford one myself, I was always hanging around the computer department in big stores for hours, typing soon-to-be-gone Basic programs into it. There were lots of other boys lingering, trying to impress their peers or learning from each other as much as possible. Has anyone had the same experience, or - more probable - have I been the single nerd to do something like this?
posted by Henrik at 9:46 AM on February 19, 2009 [1 favorite]


What is that thing? It's like a second or third-generation 64. I'll put some REAL C64 pictures up on the interwebs one of these days. Sheesh. Kids and their newfangled fancy 1541 drives.
posted by GuyZero at 9:49 AM on February 19, 2009


Did we actually type programs from printed listings in paper magazines? Shit.

Yes. Yes we did. And we enjoyed it damnit.
posted by schwa at 9:53 AM on February 19, 2009 [1 favorite]


Has anyone had the same experience, or - more probable - have I been the single nerd to do something like this?

I did the exact same thing everytime I went into a Service Merchandise store in Southern Texas.
posted by elmono at 9:59 AM on February 19, 2009


Did anyone else have a sample of Billy Idol's "Flesh for Fantasy" on a floppy? What was the story with that?
posted by schoolgirl report at 10:09 AM on February 19, 2009 [1 favorite]


Staggering Jack, I remember it by how it sounds when you're little: "EL OH EH DEE, shift-two, asterisk, shift-two, comma eight, comma one, RETURN!"

I love love love my C=64.
posted by fiercecupcake at 10:17 AM on February 19, 2009 [1 favorite]


Kept my 64 running until 1991 or so, playing Blue Max, Summer Games and the amazing Winter Games -- ski jump, bobsled, all kinds of fun.
posted by porn in the woods at 10:29 AM on February 19, 2009 [1 favorite]


What is that thing? It's like a second or third-generation 64.

They mention the classic breadbox model early on. But ditto on the drives: the nostalgia isn't complete without the original model 1541 drive. Bigger, heavier, and with as much CPU power on-board as the C64 itself; built like a tank, but drove like one too.
posted by We had a deal, Kyle at 10:35 AM on February 19, 2009


I was on the Atari 8-bit side. I started noticing scans of the old computer magazines a few years ago, & it amused me that they provided the scans as images, not text - so you had to type in the programs, just like before.
posted by Pronoiac at 10:38 AM on February 19, 2009


"EL OH EH DEE, shift-two, asterisk, shift-two, comma eight, comma one, RETURN!"

Yeah, I think that was the original way I heard it too.
posted by Staggering Jack at 10:44 AM on February 19, 2009 [1 favorite]


What is that thing? It's like a second or third-generation 64.
Exactly! I don't see the point of the Tom's article. It didn't seem adoring or mocking or even informative.
(And real C=64's aren't white)

I don't Commodore around much any more, but I was looking at this just yesterday.
But now I'm more interested in Guitar Hero.
posted by MtDewd at 10:54 AM on February 19, 2009


38,911 BASIC BYTES FREE.

You can emulate a 64 pretty much perfectly. I usually use CCS64; I assume it will work on Vista, but I haven't tried it. I have a pretty broad collection of old disk images and ROMs, too, so if you're looking for a particular thing, drop me a MeMail, and I'll see if I can find it.

It's startling how tiny these games are -- 64 floppy images are 170K. From memory, I think the actual usable space is 160K, but I'm not sure of that anymore.

And think for a second, how long it takes to load 160k on a modern machine; it's so fast you can't even detect it. You just wouldn't believe how slow the Commodore 1541 drive was. The initial load of a program could never be more than 64K -- and it would take like FIVE MINUTES to get that far. Seriously. Glacial doesn't even begin to describe it.

LOAD "*",8,1 -- and then go get a cup of coffee and take a leak, and you'll still be back before it's done.
posted by Malor at 10:56 AM on February 19, 2009 [2 favorites]


My first and only royalty checks came from an article published in Compute!'s Third Book of VIC, back when you typed in each program yourself, from printed source, and your pristine lawn was free of kids.

At the end of its run, "VIC 3" overstocks were apparently being sent back to the distributor, and I received a few statements with negative royalties, which Compute! fortunately never sought to collect.

I upgraded its RAM with a 16KB stick that sold for the equivalent of $13 million per GB in 2007 dollars.
posted by kurumi at 10:58 AM on February 19, 2009 [1 favorite]


You just wouldn't believe how slow the Commodore 1541 drive was.

I tried to show my kids a game on TAPE a few months back when the C64 emerged from the piles of moving boxes. A 1541 seems fast compared to tape.

Also, I still have 10-min long computer-specific cassette tapes. In a Canadian Tire tape holder/organizer.

If I ever get my 1200 baud Commodore modem hooked up then THAT will be nostalgia.
posted by GuyZero at 10:59 AM on February 19, 2009


Did we actually type programs from printed listings in paper magazines? Shit.

I especially remember the difference between typing in a Basic program and having some illusion that I was understanding what the program was doing and that I was maybe even learning something vs. typing in a program in "Machine Language" which was just Blind Faith and Magic.

Alas, all the best games from COMPUTE! magazine were in Machine Language.

And then came the magic day when my dad shelled out for the diskette that came with the magazine and included ALL THE PROGRAMS IN EVERY ISSUE! That day each month when the magazine came with a whole diskette full of new programs? Nerdvana.
posted by straight at 11:12 AM on February 19, 2009 [1 favorite]


Did anyone else have a sample of Billy Idol's "Flesh for Fantasy" on a floppy? What was the story with that?

Yes! I think it was meant to be a demo of digital audio recording and playback on a machine that wasn't really supposed to be able to do that. Audio on the C64 was produced by various programmable oscillators and such, so playing back an actual digital sample of music was a clever trick. I seem to recall the quality of the playback was really quite awful, though.
posted by FishBike at 11:20 AM on February 19, 2009


LOAD "*",8,1 -- and then go get a cup of coffee and take a leak, and you'll still be back before it's done.

Or just sit there, mesmerized, watching the awesome Cube-Sphere-Pyramid logo cycle through all 256 colors. For five minutes.
posted by straight at 11:21 AM on February 19, 2009 [3 favorites]


Man, who ever actually typed out LOAD to load stuff? You could abbreviate most commands by shifting the second character, (Which, instead of capitalizing, changed the letter into some funky extended character set glyph), so you'd wind up with something that looked like

LГ "*",8,1

which just made things look even more esoteric to people who weren't familiar with the machine.
posted by fnerg at 11:25 AM on February 19, 2009


Oh yeah, I spent many hours with that system. I remember reading a manual on how the C64 did its sound synthesis so I could write a basic synthesizer for it.

It had cool games too. My Apple II only had a monochrome monitor attached, so the C64 hooked up to a color TV was fantastic.
posted by wastelands at 11:39 AM on February 19, 2009


*sigh*

I loved my C=64.

SYS 64738!
posted by papercake at 11:58 AM on February 19, 2009


Yo dog, I heard you like expansion ports.
posted by exogenous at 12:25 PM on February 19, 2009 [1 favorite]


I had a VIC-20 and a C-64 and I loved those motherfucking computers with all of my heart. The hours I spent typing in programs only to have them fail because of a typo, the excitement of wondering if the tape drive would work, good times. To think I'm typing this on a 2.4 GHz Macbook Pro with 4 gigs of ram and I still miss my good old C-64. I had a budgie that I named Commodore Le Birdie AFTER MY COMPUTER!!!!!*


*The Le Birdie was just flair.
posted by Divine_Wino at 12:45 PM on February 19, 2009


Mmm, the C64. I still have 2 of them in working condition --- if I had a larger place, I'd leave them set up.

Anyone else on QuantumLink back in the day? That was my first "national online service" (as WildCardJ). $4.80 an hour, those were the days. Club Caribe (proto graphical MMO"RP"G) was the shit. I eventually paid for my online time by being a QLink beta tester and moderator -- back before they clamped down on child labor for such things (I was in middle school).

I eventually had all sorts of accessories --- even a hard drive (I think it was 20 MB, which seemed huge at the time), a voice recognition card (which was... less exciting), and a hand-built light pen. Built some joysticks and a few other simple peripherals as well, back then magazines actually had instructions for that sort of thing, just go to Radio Shack and pick up some parts and now you have a wobbly, freakish looking controller!
posted by wildcrdj at 1:07 PM on February 19, 2009


Anybody else remember the Commodore 1350 Mouse that you could use with GEOS (or try to, anyway)? Unlike a lot of other stuff that makes me all nostalgic, I just remember how horrible that thing was to work with. It emulated a joystick, so the mouse pointer could only move at one speed, and in one of eight directions, regardless of what you did with the actual mouse.
posted by FishBike at 1:36 PM on February 19, 2009


I still haven't found a single video game that's excited or scared me as much as Maniac Mansion on the C=64.
posted by PhoBWanKenobi at 2:00 PM on February 19, 2009


I was actually jealous of the C64s we had at school -- all we had at home was the 16k Radio Shack TRS-80 Color Computer. But I spent many an afternoon typing in programs from this book.
posted by evilcolonel at 3:48 PM on February 19, 2009


Everyone should watch The Ultimate Commodore 64 Talk, which gives you more information about the system in 64 minutes than you'll ever need.

And let's not forget the demoscene - geeks all around the work cranking out incredible audio and visuals on a 26 year old machine, just because they can.
posted by ymgve at 4:58 PM on February 19, 2009


Okay. I thought I was familiar with the C-64 demoscene and the crazy shit they could pull off on that hardware, but then I watched ymgve's link to Booze Design's Edge of Disgrace seriously holy fuck that shit shouldn't be possible at those framerates like no fucking way like whaaaaaaaaaaaaaaaaat
posted by suckerpunch at 6:37 PM on February 19, 2009


still remember when we bought a 1571 disk drive and what an improvement it was over the 1541

As an Applesoft guy I used to point and laugh at the C's shitty single-wire drive connection.

Then SATA came out twenty years later and I regret my past ignorance.
posted by troy at 7:30 PM on February 19, 2009 [1 favorite]


kurumi: My first and only royalty checks came from an article published in Compute!'s Third Book of VIC, back when you typed in each program yourself, from printed source, and your pristine lawn was free of kids.

I sold a good number of things to the Loadstar magazine-on-disk as a kid. Paid for my Sega Genesis and Super Nintendo that way. I really should see about posting one or two of the better games to Projects, but I'm unsure I can get the rights to them.

Henrik: Before I was able to afford one myself, I was always hanging around the computer department in big stores for hours, typing soon-to-be-gone Basic programs into it. There were lots of other boys lingering, trying to impress their peers or learning from each other as much as possible. Has anyone had the same experience, or - more probable - have I been the single nerd to do something like this?

My dad played a mean trick with me. He got me the C64 for Christmas, but he gave me the manual in July. The pages were coming out of their spiral binding long before I was able to open the box, I had read through it so much, so I learned how to program in BASIC months before touching a keyboard. I kind of wish I had that kind of focus now....

We had a deal, Kyle: (But then you saw the things that the demo coders did with it and realized that actually, there was a whole other level of mastery that you would never, ever reach...)

They had some great tricks, to be sure, but they were still tricks. They really did nothing more insane than what Atari 2600 developers had to do to make every damn game.

Blazecock Pileon:
I once had a fairly substantial collection of Ahoy!, they were quite a wonderful little magazine, not as slick as Compute's Gazette, but enthusiastic. Unfortunately they didn't survive the Great Closet Clean-Out when I went off to college.

Here's a story that I relate here as one of those little things to remind me that something I saw once actually happened, and wasn't a dream or idle fancy:

Once on a college club trip to Atlanta we went into a grocery store for supplies, and I passed by the magazine rack. This must have been early 90s, maybe as late as '93.

There, to my disbelief, on the magazine rack, was an issue of Compute's Gazette, a magazine that once had been sold on nearly every grocery store newsstand but had ceased print years before. (The last standalone issue, according to the 'Pede, was June 1990.) It must have somehow repeatedly missed getting cleared out of the magazine rack. I should of bought it, but I didn't have the cash on me. Yet another missed opportunity....

By the way, while searching for the magazine's last publication date, I ran into this Pirate Bay page that offers a torrent that purports to have PDFs of every Gazette issue.
posted by JHarris at 2:36 AM on February 20, 2009 [1 favorite]


Henrik: Before I was able to afford one myself, I was always hanging around the computer department in big stores for hours, typing soon-to-be-gone Basic programs into it. There were lots of other boys lingering, trying to impress their peers or learning from each other as much as possible. Has anyone had the same experience, or - more probable - have I been the single nerd to do something like this?
I had an Atari 400 at home, & I typed in the same BASIC program at a store on a couple of other computers (800? 1200XL?) to benchmark them & see if they were any faster.

I don't remember the results, but I remember the (really slow) algorithm I used to list prime numbers, & that embarrasses me more.
posted by Pronoiac at 9:05 AM on February 20, 2009


They had some great tricks, to be sure, but they were still tricks.

Oh, for sure; but to this 14-year old they were nothing short of magical. Sprites in the border? What-what-what? That certainly wasn't in the Programmers Reference Guide.

And in 1984 it wasn't as if you could hop on the Internet and google up a how-to guide. I knew just enough to know that it shouldn't be possible. (Do such guides exist today? I'd still like to know how it was done; was it some subtle timing exploit that hit the VIC-II on just the right cycle?)
posted by We had a deal, Kyle at 10:41 AM on February 20, 2009 [1 favorite]


If anyone's still interested, I found that I have a batch of magazine disks as well as commercial disks. I appear to have 64-er magazine disks from 84-94, Compute Gazette from 85-93, and some Loadstar disks that appear to be more or less a random assortment. I see 15-20, 24, 25, 30, and 59. 59 has four files; it looks like two double-sided disks. The others are all two files.

I know absolutely nothing about these, but if you do, and want a copy, let me know.
posted by Malor at 10:50 AM on February 20, 2009


Henrik: Before I was able to afford one myself, I was always hanging around the computer department in big stores for hours, typing soon-to-be-gone Basic programs into it. There were lots of other boys lingering, trying to impress their peers or learning from each other as much as possible. Has anyone had the same experience, or - more probable - have I been the single nerd to do something like this?



heh - you're not alone - i had an i am a future customer speech as well for the store assistants that seemed to work lol


(another vote for the mighty spectrum btw - both computers have a faster startup time than my laptop)
posted by sgt.serenity at 5:45 PM on February 20, 2009 [1 favorite]


In 1982, I had myself a VIC-20 with a 300 baud modem, a roomie's C-64 and lots of games and accessories. The best thing by far was my free and unlimited access to his CompuServe account when his Navy ship was out to sea for months at a time. It's no wonder I'm still addicted all these years later. :)

The C= was a lot of fun, but the Commodore Amiga was the best computer ever. And it was very good to me. I met my now-hubby on FidoNet's AMIGA message board (you know, land line modem dial up every day over POTS wires) back in 1995. We're still together. :)
posted by keptwench at 9:13 PM on February 20, 2009 [3 favorites]


I'm saddened Jim Butterfield died before he could see this post.
posted by JHarris at 9:08 PM on February 21, 2009


Oh, for sure; but to this 14-year old they were nothing short of magical. Sprites in the border? What-what-what? That certainly wasn't in the Programmers Reference Guide.

I know how they did it. This is purely from memory, but I seem to recall doing it once. I heard about it from somewhere else, I think. Keep in mind, the time during which I would have done this is over 15 years ago....

(Memory location info comes from my copy of MAPPING THE COMMODORE 64 & 64C by Sheldon Leemon, the rest from memory.)

In the recesses of the VIC II chip that's contained within every C64 is a pair of bits that control the border width, at the edges of the screen of the screen. They are bit 3 of 53265 ($D011) and 53270 ($D016). The first is the vertical border, and the second is the horizontal.

When set to 1, the vertical register switches the screen from 25 rows to 24, and the horizontal register switches it from 40 columns to 38. This is done by extending the border in by a few pixels on each edge.

The purpose of this is to cover up scrolling artifacts. These registers also control pixel-level positioning of the text screen. During normal operation, the scroll registers are centered, but if one is set a little off, the gap between the text screen and the border will be empty space. By extending the border a little, it'll cover up the space and make it appear that the characters are sliding in seamlessly from behind the border.

Now, the VIC II chip contains a raster interrupt feature. If enabled, it will trigger an interrupt when the television scan bean reaches an arbitrary line on the screen. This is activated by writing a 1 to bit 0 of 53274 ($D01A), and the line selected by writing it to 53266 ($D012) and the high bit (the range of values is a little more than 255) to bit 7 of 53265 ($D011).

Now stop a moment and consider this. The screen shrinking is done by extending the border a little outward. It'll actually grow by a few pixels on the edges. Internally, the VIC II does this for the vertical border by watching for the proper scan line to show up, then turning the border off. When the line reaches the bottom of the screen, it'll turn it back on, again at the proper line. What changing the border size effectively does is turn the border off a little later, and turn it back on a little earlier.

But what would happen if, after the point the border were to be turned back on while shrunk was passed, but before the point where it is turned off when at normal height? There's a three-or-four line leeway between the two, when the raster beam is in that section of the screen that's blanked when the border is expanded, but shows text when it's not. If the border size is changed from normal to expanded in that time, then the border turn-on never occurs! It'll be normal when the expanded checkpoint is reached, so it won't be turned on there, and it'll be on when the normal checkpoint is reached, so it'll think there's no need to turn it on there either. Ot'll remain off all the way through VBLANK, to the point where the beam comes back in at the top of the screen and sweeps all the way down through the screen. The screen will need to be switched back to normal height at some time after the upper border would have been drawn, but there's a whole screen through which that can be done. It could be done with another interrupt set to any old place.

The border is never turned on, so it shows the background color in that area. The screen cannot display characters in that zone (the chip designers never expected there to be a need for it), but it can display sprites.

I believe this trick works for the horizontal borders too, but there's much less leeway in timing, especially since there is no horizontal version of the raster interrupt. You'd basically have to do it Atari 2600-style, racing the beam, and the C64's processor is actually a little slower than a 2600.
posted by JHarris at 7:02 PM on February 22, 2009 [4 favorites]


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