question for multigame designers

brzezicki

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Hi, I have a question for the multi game designers out there.

most multi games I've seen like the braze kits have a method of switching games on the fly (like pressing p1 and p2 at the same time)

while I understand how to do that (basically bank switch ROMS and cause a CPU reset) I don't know the most effective way to do so so I'm interested in opinions.

I'd think the cleanest solution would be to tap P1 and P2 into a custom circuit that monitors for the key presses, then you don't have to modify the ROMs at all so the game is basically 100% original in terms of code.

however to do that you'd need to have the p1 and p2 buttons go to the multi game board so your custom circuit can monitor it, I have not seen any multi games that do that though.

the other obvious solution I can think of is doing it in software by adding a check in the input loop to see if both buttons are pressed down, and if so then triggering the circuit above to do the bank switch and reset. however to do that you would obviously need to modify the game code for each game, which while not hard seem like an un-necessary pain as well as slightly altering the game code which seems undesirable for this community that's so stuck on 100% originality.

based on the multi-game kits I've seen I'm assuming they all do the code modification route as none of them route P1 and P2 controls through the multi game board kit.
are there any other methods that I'm not thinking of?

-thanks
brian
 
You could have circuitry that snoops the address and data lines, and grab the data directly from that every time the CPU reads the controls.

DogP
 
Some multi games are doing as you suggest, see http://www.seanriddle.com/newmg.html for one example. There's also times where you are going to NEED to patch the code anyways as there's typically slight differences in the hardware that require patches (if using orig HW) OR using an FPGA to replace the hardware you can accommodate these differences by actually changing the "hardware" when you switch games. Other functions like ADDING high score saving, or allowing "soft" control of dip switch settings etc. may require code patches as well. I guess it depends on what the goals are that drives the decision of how to do the switching.
 
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