Re: Sega Multigame (and cheats)

Clay wrote:

>Hmmmm. One thing I didn't try-- complement the data word. Better
>give that a shot... ;-)

You know, as soon as I wrote that I knew that was the fix... Tried it at
home over lunch and it works. This is a the snippet from main.c in Al's
source with my changes (and addition of warp and photon support):

-------
                 case STARTREK:
                 case TACSCAN:
                 case ZEKTOR:
                  if(outRegF8 & 1){ // if we're reading the switches (0xff)
                        c = 0;
                        if(start1) c |= 0x01;
                        if(start2) c |= 0x02;
                        if(fire) c |= 0x04; // CNC 10-14-97
                        if(thrust) c |= 0x08; // CNC 10-14-97
                        if(warp) c |= 0x20; // CNC 10-14-97
                        if(photon) c |= 0x10; // CNC 10-14-97
                    return(c);
                  }
                  else {
// if we're reading the spinner (0xfe)
                   if(left) { spinner+=10; dir = 0; } // CNC 10-23-97
                   if(right){ spinner+=10; dir = 1; } // CNC 10-23-97
                   return((~spinner << 1) | dir); // CNC 10-23-97
                  }
-----

I'm adding 10 to the spinner count just because it seems like a good
"playable" value for Star Trek and Tac/Scan, dunno about Zektor. I'd
suspect it's alright.

I don't have a great explanation why that works. The only thing I can
think of is that there's an inverting buffer somewhere that's changing the
output from the 74LS393 on the single player control interface. My
schematic says it's using a 74ls244, but maybe they're populated with
74ls240's?

Anyway, this works.

-Clay

Clayton N. Cowgill Engineering Manager
_______________________________________________________________________
/\ Diamond Multimedia Systems, Inc. clay@supra.com
\/ Communications Division http://www.supra.com/
Received on Thu Oct 23 14:22:24 1997