Re: Dating a C-64 board

From: Marko Mäkelä (
Date: 1999-04-23 08:27:07

On Fri, 23 Apr 1999, William Levak wrote:

> Four sprites on the same line cause the disk drive to hang up when
> loading.
> They can be the first four, the last four, or every other one, it doesn't
> make any difference.

Actually 2 or 3 sprites should be enough, if they are not successive ones.
As you can see from the timing diagrams in the document
<URL:>, the
timing of a bad line without sprites will be like this:


The diagram is for the 6569.  On the 6567R56A, replace "++" with "++++".
On 6567R8 and later, replace it with "+++++".

The BA line will be made inactive 3 cycles before the DMA takes place.
That'll happen after the 2nd "r" (refresh cycle) on the left.  If sprite 0
is active, the processor won't get any cycles after the character fetch on
PAL systems (the 40 cycles marked with X), or it'll get 1 or 2 cycles on
NTSC systems.  Considering the 3-cycle rule, it won't make any difference
whether you have sprites 0..3 active, or just sprites 0,2,3 or 0,1,3: the
processor won't get any time unless the DMA will pause for longer than 3

I think that activating e.g. the sprites 0,2,4 or maybe even 0,3 should
hang the protocol.


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