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Cybernator
Registered: Jun 2002
Posts: 154 |
VIC features at 2MHz
I'm curious as to how 2MHz change things relating the VIC features/timing. As the DOT clock is exactly 8 times the phi-2 clock, two things can happen:
1. Increase the DOT clock to 2*2MHz (~16 MHz), so that the nr. of cycles per frame doesn't change, but we have faster screen refresh.
2. Leave the DOT clock at ~8 MHz, and have more CPU cycles per rasterline.
Now that I have access to a C128 (:-DDDD) I can see the first case is incorrect. (*)
Since on C64 I can _move_ the write access in 8-pixel steps, that means on C128 I can do that in 4-pixel steps. On the other hand, VIC's I/O accesses are synced to the phi-2 clock (which is now at 2 MHz), not the DOT clock. That would mean there're still 63 cycles per rasterline, i.e. the second case is wrong as well, but then the first case would have to be correct. ;P
Another possibility is to leave VIC at 1Mhz, while the CPU is at 2MHz. But then there would be access-conflict between VIC and CPU, I guess.
Hope you understand what I'm thinking of. ;)
Btw, the CPU clock on C64 is not exactly 1 MHz, but 0.985 MHz (IIRC). Thus I guess the CPU clock on C128 is not exactly 2 MHz. So what's the exact frequency then?
Also, are there any VDC features?
Would be cool to do something with this monster sometime. ;)
Btw2, how can I use CPM? Is there a disk image available for download, and can it work with a 1541? Is there anything cool I can do with Z80 that I can't do with 8502?
--
(*) Though I'm not exactly sure
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Monte Carlos
Registered: Jun 2004
Posts: 351 |
I forgot to say, that i was refering to Uridium.
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
$D030 was well known in 1986 already because the 1001 Crew had an ESCOS routine which didn't work on C128 due to overwriting $D030. They had to fix their routine. Also some of the old games suffered from the same problem, for example "Masters of the Universe" or "Rescue on Fractalus". |
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Oswald
Registered: Apr 2002
Posts: 5025 |
Graham:
"1. c128 wasnt as widespread"
Not quite true, C128 was pretty common. Ofcourse far more C64s existed but compared to other machines like Atari XL or Amstrad there were more C128s out.
- my argument is still true: wasnt AS widespread (as the c64)
"2. the hardware is not really superior. VIC is more powerful in most of the cases than VDC, but then you dont have 2mhz. If you want 2mhz you have to use VDC, but the VDC is 3-4 times slower to write."
Also not true, you can easily use the 2 MHz mode if you use VIC display. There are several C64 games which use that, for example Uridium which uses 2 MHz in the border area and handles more enemies because of that.
- only on the top/bottom borders. I had true 2mhz in mind when formulating that sentence.
my conclusion is still:
c128 wasnt superior enough to open a new scene. c128 was mainly used as a c64clone. |
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raven
Account closed
Registered: Jan 2002
Posts: 137 |
@Oswald: 2mhz in the borders is still great & gives a very
nice boost to math-based effects.
In the Tunnel effect in Insomnia i use 2mhz in the border
and the result is nearly twice the update speed.
@Graham: afair, HawkEye also wrote on $d030 when copying
vic registers from a table. It was fixed in some of
the cracks that were released. |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
Yeps, all the games/demos I've seen which had the $D030 bug had this kind of bug. They all copy a table to the VIC registers, but don't stop at the last C64 register ($D02E) and continue with $FF or some other memory contents.
@Oswald: There was some impact the C128 had. Many programs use it's advantages. It's a bit like on other platforms like Atari 800XL vs Atari 130XE or Amstrad CPC464 vs CPC664. Most programs were written for the "smallest" machine of a platform since it offered the biggest amount of buyers. Some programs had advantages when using the "bigger brother" though. This is not different on C128. You should not see the C128 as an own platform because it isn't, the C128 is just an extended C64 and that's how people used it. |
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Nafcom
Registered: Apr 2002
Posts: 588 |
Quote: Yeps, all the games/demos I've seen which had the $D030 bug had this kind of bug. They all copy a table to the VIC registers, but don't stop at the last C64 register ($D02E) and continue with $FF or some other memory contents.
@Oswald: There was some impact the C128 had. Many programs use it's advantages. It's a bit like on other platforms like Atari 800XL vs Atari 130XE or Amstrad CPC464 vs CPC664. Most programs were written for the "smallest" machine of a platform since it offered the biggest amount of buyers. Some programs had advantages when using the "bigger brother" though. This is not different on C128. You should not see the C128 as an own platform because it isn't, the C128 is just an extended C64 and that's how people used it.
According to Bil Herd in the Commodore book at http://www.commodorebook.com, in the C128 chapter, the C128 was meant as a real successor to the C64 and as an own machine, not as an extended C64. However Commodore closed down the software department and no other company wanted to produce C128 only games, since the C64 received more customers.
Bil speculates, that if CBM wouldn't have closed down their software department, the C128 would have received more support from other software producers. |
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Oswald
Registered: Apr 2002
Posts: 5025 |
raven, graham: ok, it's hard to argue, when you forgot what it started it all, the question was that why the c128 havent had a scene.
2mhz is nice in the borders, but 150% cpu power is still not THAT much to make ppl leave c64 for the c128.
Im not against c128s, I havent said it got no impact.
I:"c128 wasnt superior enough to open a new scene. c128 was mainly used as a c64clone."
Graham: "you should not see the C128 as an own platform because it isn't, the C128 is just an extended C64 and that's how people used it."
ok, so whats the point telling me that, I think the same, have you really read my post ? :(
Please stop acting like I am attacking the 128. In fact during my scene career all demos until and including soiled legacy was written on a 128d. I have nothing against the platform, in fact I love my 128. |
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Graham
Account closed
Registered: Dec 2002
Posts: 990 |
Well thing is that the C128 IS a C64 clone and not just used like one. Now you may call me a hairsplitter :D |
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Oswald
Registered: Apr 2002
Posts: 5025 |
this is pointless, let this topic sink. |
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BastetFurry
Registered: Jul 2005
Posts: 88 |
Quote: the c64 mode is 99,9% compatible with the c64, there are 2 differencies. You have 2 extra registers in the vic, d02f to read the numeric keyboard, and d030 for 2mhz mode and its test bit. Then you have the VDC registers also mapped in.
You change to c64 mode with the mmu (afair). simply there's no way to have the mmu visible in c64 mode. but the only difference between c64 and 128 mode is the mmu visibility and different rom set imho.
Umm, he gets another 5% Minus from me, mp3@64 dosnt work and sometimes the MMC64 behaves very strangly. |
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