Re: [stella] RESPx and player positions

Subject: Re: [stella] RESPx and player positions
From: Eckhard Stolberg <Eckhard_Stolberg@xxxxxxxxxxxxxxxxxxxxx>
Date: Mon, 20 Apr 1998 17:20:05 +0200
At 09:36 19.04.98 -0400, you wrote:

>My initial guess was that if you do a STA to RESP0 then the counter is reset 
>to 0 at the end of the STA and the counter decode circuit doesn't see this 
>as a 0 crossing count.  However, it would seem to me that doing an RESP0
>during HBLANK (as trick.a65 does) would end up showing the 1st player 
>but it doesn't.

TRICK.A65 doesn't do the RESPx during HBLANK. The first RESP0 ends
at cycle 22. This seems to be already part of the display, since
cycle 22 is the first cycle, at which the trick works.

Also, in the 15 sprite version of trick.a65, take a look at the 
second sprite from the right. It is displayed 2 pixel more to the 
left. This happens with all sprites, that don't have another sprite
hitting the same RESPx register in time. Replace some of the 
STA RESPx in the middle with STA $86, to see, what I mean.

>A few more questions on players :-)
>  1) Has anyone tried changing the graphics of a player while it's being
>     scanned? 

I don't know the exact timing, but it is possible to hit GRPx
so, that some of the old and some of the new data is displayed.

Ciao, Eckhard Stolberg

Archives (includes files) at
Unsub & more at

Current Thread