Monday, October 30, 2006

XeO3: C64 time....

I got my new dual parallel port today, so I spent the evening updating the Plus/4 downloader to allow me to change port address, and writing the new C64 downloader. The piccy shows the new cable before I've tidied it all up and put the casing on; but now that I know it all works, I can do that whenever.

The C64 cable is cool as it sets a whole byte at once (unlike the +4 that sends nibbles). But it only seems to match the +4 speed, probably due to the higher clockspeed on the +4. I suspect I could knock a second off the +4 one if I blacked the screen, but 6-7 seconds for 64k is quick enough. This should allow a quicker turn around of testing on the C64 version as it downloads under the ROM's and VIC chip, which in turn means I dont HAVE to pack it to run/test it.

Once I've cleaned it all up I'll post the new C64 downloader, along with the wiring diagram - although I suspect its the same as a few others, its very simple: 8 Data wires, 1 signal, and 1 busy - easy. I know loads of folk will simply point out that theres already 1,000,000 downloaders, but from what I saw, they were all far too complicated - I just want download and run!


Chicken said...

In addition to switching off the screen, switching to NTSC would speed up the plus/4. It's "ugly" but it works. I did this with a floppy speeder and for huge files you could notice the difference.

Though, I agree... 6-7 seconds is fast enough. But for kicks, I'd like to see benchmarks ;)

Have you ever found out, what happened to the parallel port? It's really weird that just one line is defunct.

Mike said...

Why is NTSC faster? Do they increase the clock speed? I thought it was just less TV lines to draw on the +4, so it ran through frames quicker - which woulnd't change the number of cycles per frame being processed.

Yeah, I suspect that since I got the diagrams wrong, I wired a 5v to one of the IN's on the port - not a good idea.

But now I have both +4 and C64 plugged in at once, which is cool. I was thinking, what I really want.... is a USB->Parallel port. This would make it easier for folk to use, and while it wouldn't be any quicker (since its still the parallel port), would make it a bit more compatable with modern machines. (most new PC's dont even have a parallel port).

Chicken said...

It's still a PAL plus/4, not a NTSC machine. By setting the NTSC mode bit you choose a different chrystal clock divisor. That's why it's faster. This also increases the dotclock, which is one of the reasons why 50/52 char effects previously discussed on plus4world are possible.

Some apps use the NTSC mode... turbo loaders, packers/crunchers and even some digi playback routines. I wouldn't use it for anything that you "see" because it screws up the display. But for number crunching and calculations etc it makes sense if you have to do that on the real machine.

A couple of month ago I borrowed an "USB to PARALLEL PORT" cable from a friend. I guess it was a printer only cable, though. I tried hooking up my old parallel port zip drive (using an centronics to subd adapter), didn't work... same for a parallel port scanner. So I'm not sure if one of those would work for you.

And those cables are pricey. It's cheaper to buy a parallel port card.

USB would be great, I agree. I remember how everyone moaned about it back then but it's one of the few things I really like about PCs.

Atari 8bit freaks implemented some USB stuff. It'll be cool to have that on plus/4, too. Though, I'd be perfectly happy with MMC/SD.

Chicken said...

If you want to turn a PAL plus/4 into a NTSC plus/4 you need to change the crystal (and replace the ROMS).

In PAL mode the crystal frequency is divided by 20 and in NTSC mode by 16.