Re: Secret programs

From: Richard Atkinson (
Date: 1999-08-01 02:43:55

On Sat, 31 Jul 1999, Steve Judd wrote:

> It might be worthwhile to upload a copy of the sfx 26/2 file, for people
> not using emulators/star commander.  The disk has a little extra
> protection on it in that byte 2 of 18,0 -- the DOS ID byte -- is set to
> $45, not the normal $41, so that sector editors run on a real 64 generate
> an error 72 when writing to the disk.

Is it completely impossible to get at it? I would have assumed that
anything a PC can do with a 1541 a C64 can too.

> Also, to NTSC-fix the file, change location $C0A8 to $24 after loading :). 

Thanks, that's worth knowing. I'll write a little text file to accompany
the demo disk, with hints to that effect.

> On a different topic, I just hooked up my very first 64 to my normal
> monitor, and the display is very different than my 128's display -- the
> colors are somewhat washed out, the pixels not as well-defined, etc.
> Is this a known phenomena?  It kinda looks to me like the luma and chroma
> aren't split -- do older 64s use a strictly composite signal?  Just
> curious, as I've never seen this before.  (This is using my normal cable,
> my normal monitor, etc.).

OK, there are two issues here. Whether you have a _very_ early C64 with a
five pin DIN video socket (so it doesn't have a Chrominance pin) or
whether you have a C64 with a 6567R5 or 6567R56A. I'm guessing it's the
latter, since you mention using your 'normal' cable.

Colours being washed out simply means the chrominance has low gain. You
can compensate for this easily by turning up the colour control. Pixel
definition is a more complicated issue that usually only turns up with
composite displays. However, I have seen a lot of leakage of the
chrominance signal into the luminance channel on Commodore displays, which
leads me to suspect it is the same problem.

In that case, the issue is this: 6567R5s and 6567R56As have 64 cycles per
raster line. Since the dot pattern used in the colour encoding process
repeats itself after two cycles, it appears entirely static on the screen
as fine vertical stripes. This makes the pixels look indistinct, and can
cause single dot pixels (surrounded by background colour) to disappear.
Hence the Character ROM has all horizontal pixel widths no less than 2.

6567R8 and later were changed to use 65 cycles per line and 263 lines per
frame. This causes the pattern to alternate every line, but because of the
odd number of lines it also alternates every frame. In this situation, the
pattern is more like a chequer board, and since it is alternating at 30Hz
it all but disappears.

That is on NTSC. PAL is a different story altogether :)


This message was sent through the cbm-hackers mailing list.
To unsubscribe: echo unsubscribe | mail

Archive generated by hypermail 2.1.1.