Re: 6510 and 8500 differences

From: MagerValp (
Date: 2000-08-09 18:48:56

>>>>> "M" == MagerValp  <> writes:

M> Press space when the 26-line scroller asks you if you want an
M> explanation of the 26-line bug.

Extracting the scroller with VICE was pretty easy, so:

Okay, here is the detailed explanation of a VIC-bug, which is quite
different from the other ones. Let's get concrete: you might know that
a read-modify-write instruction of the 6510 has two write cycles. In
the first one the original data is written again, only in the second
one the updated data is stored. If you now use such an instruction at
the beginning of the first border-line, so that within the first
written cycle the border is active, but within the second it is
disabled and(!) there is a badline condition, the VIC gets totally
confused and displays a 26th charline. As the internal screen-ram-
counter is just 10 bits wide, the data for this line wraps from $03e8
to $000f. however, there is a drawback. I don't know what's happening
inside the VIC, but it's a fact that the chip gets unusually hot while
using this effect. But don't worry, i included a check which will
prevent your hardware from damage. How does this work? Easy, higher
temperature results from higher current floating through the VIC. Now
you know, that the four upper bits of the color registers are random.
This is true, but they also depend on the amount of electrcity inside
the chip. More power means, it is more likely that a bit equals 1. So,
if there are four different $d02x-registers having bits 4-7 set, then
you know it's time to deactivate your computer. As mentioned, such a
check is included in this part. That means, don't panic :) Okay, this
was a lot of text, so i'll take a break now. Cya!

I think this was written by Ninja/Tempest, but I'm not sure.

PS: VICE doesn't display the raster behind the scroller correctly,
    possible bug. The VICE developers read this list, right? :)

    ___          .     .  .         .       . +  .         .      o   
  _|___|_   +   .  +     .     +         .   .  Per Olofsson, konstnär
    o-o    .      .     .   o         +
     -       +            +    .
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