Posted by Druin on 10, 2000 at 10:27 AM:
In Reply to: Ooops, I forgot about the 0&0=1 state posted by Yehonatan on 10, 2000 at 4:57 AM:
:it's probably more practical/convienent to have an "electric" solution than a "mechanical" solution.
Don't forget also about software solutions - MAME can allow you to implement this type of logic for each game, so you can just have the 8 way joysticks sitting as-is with no modifications or hardware logic added, and for each 4-way game, you just configure the joystick inputs to lock out diagonals.
I don't remember how to do it but it's been discussed here (that's how I found out about it).
Otherwise, just for fun, I'm going to right now on the spot try to think of a possible hardware logic solution to the NAND problem you had. Let's see...if you use an exclusive NOR (I forget if those exist or not, if not, just an inverter on an ex-OR) with the 2 directions belonging to a diagonal at the gate inputs, you'll get an output that is high when at least one, and ONLY one of the diagonals is activated.
You can use that either to go along with some other logic inputs for the individual joystick directions, OR you can use them as enables on a buffer, ie you run each of the 4 joystick microswitches to a tristate buffer that will pass their signal when the chip is enabled, or disconnect the microswitches when disabled...
So you have 4 Ex-NOR gates in total, that is, an output for each diagonal direction, showing when only one of the 2 directions of that diagonal are active at a time, and you tie those 4 ex-NOR outputs together, and run them to a tri state buffer chip's Enable line (invert if necessary to get the proper enable active logic level). On that buffer chip are the individual direction switches also.
At this point I can't remember why I said ex-NOR and not ex-Or, I haven't slept in a while and if there was a reason..who cares, I think it all comes down to the input signals being active low ground signals or something. blah.
If tri state buffers aren't to be used, then how about simply AND gates (or NAND or whatever it takes to "and" two signals of our active low or high nature, from either the microswitch grounds or the other exNor outputs). So you have the exNor outputs, and you AND them with each normal microswitch direction and get 4 new master outputs from the AND gates. The AND outputs will only be active when the given 4-way direction is pressed AND only one of the 2 possible diagonal directions are pressed. So. If we are talking about up and right as a diagonal here, you have the exNor 2 inputs from Up and Right. Then you have two AND gates. Both have one of their inputs tied to the ExNOR output. The other AND input is connected to the UP switch on one gate, and the Right switch on the other AND gate. When you press UP, you have the ExNOR output active to show it's only one of the 2 diagonal directions, and you also have the other input of that AND active because you're actually pressing the UP switch tied to it.
If you press up-right diagonally, you get nothing because although the AND input tied directly to UP is active at this point, the ExNOR output is dead becuase you've got more than "just one or the other" input of the ExNOR active.
I'm babbling but there's 2 ways I think will work IF you choose not to use the built in MAME logic!