Dual Boot R-Type 1 & 2 Arcade PCB - Day 3
Here's the circuit I would need to correctly select between two Rom chips - using a single hi/low "game select" signal:
(I made a mistake with my first Rom-select design (The NOT & AND gate thingy) in the first post)..
The /CS (chip select) line on the Roms activates the chip when it goes low..!
So here, I use two sections of a 74157 to pass either the hi/(active)low /CS signal (or) a 5v signal.
This should correctly disable the unused Rom chip with the positive signal while passing the /CS to the other one.
Just programmed the 27C040 ROMs for C0-3 & N0-3, wired up the A18 address pins to the previous orange wire patch and observed the following:
* R-Type 1 is still fully functional (as expected).
* R-Type 2 has some visual errors, which are related to the extra electronics & board modifications...
** Minor erroneous background tiles.. Not bad, but a few wrong (similar in nature to RT1 prior to the logic/board mods).
** All sprites are a block of solid colour.
So it looks as if I will have to add those multiplexers to switch the modifications in & out.. cool. :)
Also have to do something with the audio Rom.. And since I'm going to use those multiplexers, I think I'll go with the new Rom selection logic above (and be switched with all the other board signals).