My niece gave me a bunch of old PC boards, one being a ISA bus sound card. And - it had a 74LS245 on it, although not a DIP package. Well, that works for me - I wired it in to the design (instead of a 540) and only to /CE0. I will wire both /CE0 and /CE1 when I find a 74LS08. Well, I may be able to wiring in both using diodes, but I need to do some research.
The 74LS245 hot glued to the interface board and
blue wires attached to the 'B' side of the chip.
The 74LS245 fully wired into the design.
Success! This is T-Tris, running on the new setup.
So, with the 74LS245 incorporated, I don't have to do a bunch of weird 'bus switching' code in the PIC. It simplifies the code dramatically, which is needed. Next is to incorporate either the USB for reading game images from a thumb drive, or an SD Card slot. OR figure out how to increase the storage capacity of the PIC some other way (right now it's 32K bytes minus 256 bytes for code and 64 bytes for a header).
Games running so far:
2) Karri's PONG
I still haven't managed to get the BLL loader working. BUT - I _can_ load either pure cart images, 'LYNX' header images (for emulators) and 'BS93' images (again, for emulators).
New ROM Emulator schematics, V1.01 (5 pages). Now I need to find the parts - how am I going to find a 74LS540 and a 74LS08 around here? Time to scrounge at the local repair shops.
I need to add a tri-state buffer to the data lines, that is enabled when either CE0/ or CE1/ go low. Right now the PIC drives the data lines continuously and this messes with the buttons - and who knows what else. There is a tristate (TRISD) for the data port (PORTD), but I can't switch it around fast enough to present the data to the Lynx. GRRRR. I have a timeout method for tri-stating the data port, but I'm unsure if I am messing up anything else in the system before it tri-states. GRRRRR. Oh well, what's a 20pin part amongst friends?
Two things: a new Game Cartridge document and a schematic for a cartridge that will allow you to emulate whatever ROM you want, plus read ROM images from a USB thumb drive.
Note: The previous versions of the Game Cartridge document have been removed as they were flawed and presented incorrect information. There's enough bad information out there, I don't want to add to the confusion.
Also note: the ROM emulator hardware is not fully tested yet, not has all of the software been written. That will come in the future.
Here's the ROM emulator schematic V1.00 (5 pages):
And here's the new Game Cartridge document - V1.02 (10 pages):
Previous updates and the original post below the break.