Re: [stella] 7800 ROMBlaster Schematic Done

Subject: Re: [stella] 7800 ROMBlaster Schematic Done
From: Kevin Horton <khorton@xxxxxxxxxx>
Date: Tue, 25 Jan 2000 01:27:51 -0500 (EST)
At 18:19 1/24/00 +0100, you wrote:
>>This circuit was designed for a 32K ROM, though it should work on 8, 16, and
>>32K ROMs. (I also assumed 8000-ffff was cart space.  Correct me if I'm wrong
>>on this (so I can fix the circuit and code example)
>
>The cart space is $4000-$FFFF.

OK, not a problem

>Is $3f a special register for your circuit or are you trying to write
>to the 7800 state control register? If it's the later, I think you are
>aiming a bit too high. This register can only be accessed through addresses

OK, I didn't remember that.  been a long time since I've dorked with the
7800 and I was going by memory.  Yeah, replace 3F with say, 00.

>The correct value for locking in a 7800 game with full MARIA and RAM
>support should be %0000 0111.

I was going by memory and the schematic again. :-)  

>>             And the vectors will need to be located two places in the ROM-
>>             one with A12 and A14 both low. (AFFC, AFFD for the reset
>>             vector.)
>
>But then the game ROM would have to be at least 32kb, right?

Naaah.  The only stipulations are:  The "blaster" code be in 8000-ffff, where
A12 are A14 both low, and A15 is high.  

Thanks for the input!


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