I was quite happy with how Phase 1 of my JJ65C02 project ended up. I had a pretty solid miniOS coded up. I had ported EHBasic to not only my system but also to the (more robust) ca65 development system, and removed hard-coded addresses allowing it to be ported, and run, on any 6502-based platform. I also had full RS-232 capability and a working and solid YMODEM implementation that I could use to download pre-built binaries to RAM. I even had some rudimentary sound capability. All in all, I had taken this stage of the design where I wanted it to go. And so I was able to spend a LOT of time using the platform and running BASIC programs on it as well as native 6502 apps.

But as I did, I started getting the itch to start improving the hardware again, so much so that now I'm starting Phase 2 of the design in earnest. This promises to be a pretty significant change.

First of all, I plan on removing support for the LCD screen and the directional buttons. They take up a lot of real estate on the board and they simply aren't worth keeping around anymore. This means, of course, that I need a new primary user interface. Now I could continue to simply use the serial interface but I've come around and decided that the logical next step really is adding in PS2 keyboard capability and some level of VGA output.

My goal has always been to be faithful to the true retro nature of the project and so I've avoiding moving much capability to "modern", high-performance chips. But on the other hand, even old-school 6502 computers would used, when needed, specialized chips for video or I/O, and so it really doesn't feel like cheating all that much, if I handle the design carefully and in the spirit of retro. For the PS2 interface, since the design already includes a ATMEGA328, I'll leverage that. But the choice for VGA output isn't so clear.

I see 3 main possibilities:

• FPGA
• Raspberry Pi PICO
• Arduino Nano RP2040 Connect

Each has their own pluses and minuses, but I'll leave a more full discussion of all that for its own separate post.

The on-board speaker is also being dropped. Again, its a non-insignificant real estate hog on the PCB and I already have an audio jack output. I'll also be dropping the 9V input and move to a USB power port for native 5V coming in. And finally, I'll be likely moving from discrete logic chips to the ATF22V10C for the address decoding (and other signaling functions).

In addition to these "improvement" changes, I'm also going to add in support for RAM banking (8k banks) to support more complex programming requirements. This necessitates a change in the memory map (which is one of the reasons behind the move to the ATF22V10C) which I'm still mulling over. I'd like to have more than 32K RAM dedicated, but it makes the address and chip/bank selection logic quite nasty.

Off we go.