Re: [stella] Strange RIOT(?) register writes in Star Ship?!?

Subject: Re: [stella] Strange RIOT(?) register writes in Star Ship?!?
From: Glenn Saunders <cybpunks2@xxxxxxxxxxxxx>
Date: Thu, 29 Aug 2002 22:56:41 -0700
At 09:34 PM 8/29/2002 +0200, you wrote:
There are three unused bits in SWCHB. If you set these to output
you can read back whatever you write to SWCHB. So you could consider
them as three bits more RAM, if you will. In the upper example it
seems that the state of "gameOffBool" is stored in bit D4 of SWCHB.
I suppose it's used to check if the game is off at the same time
as the RESET or SELECT switches are checked.

Wow. I thought you couldn't get away with using any of the VCS registers as general RAM storage. I remember asking about this a long time ago and the general concensus was that it wouldn't work.

Are there any other exceptions besides this??

Those three extra bits might be the difference between being able to do a game with the standard RAM of the 2600 and not being able to do it.

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