This is the 8x8 font I use:



I'm just getting into the world of FPGAs myself, so this is all very interesting and relevant to me - thanks!

-Gordon

very interesting! 192 Macrocells and it directly supports Verilog without the need for POF2JED like the ATF15xx series does.
though it doesn't appear to be sold anymore (atleast on mouser) and other sites like UTsource it costs between 4 and 6 EUR/USD per IC.
another downside is that it only runs at 3.3V maximum, so you would need to build your whole system around that or use Level Shifters.

so far i've made 2 VGA Controllers that barely fit into an ATF1508 using Verilog:
one that uses bitmap graphics (320x200 using 640x480, at 1BPP, you can choose 2 out of 64 colors for the whole screen)
and the other uses Tilemap graphics (320x240 or 40x30 Tiles, using 640x480, still at 1BPP but you can choose 2 colors per Tile out of 16 colors total)
both of them use a single 8kB Dual Port RAM IC to interface with a 65C02, i've been trying to find a way to avoid the need for DPRAM but i can't really fit any kind of interface logic into the CPLD that would allow me to use normal SRAM.

i have also been thinking about using SPI as an interface between a VGA Controller and a 65xx system using 65SPI. it would allow for a 3.3V VGA Card using a more modern CPLD or FPGA as you only need to level shift the single direction SPI lines (plus an Interrupt line)
hmm, something to think about i guess.

for an ASCII compatible character set i have just been using this:


either way i hope to see more experimenting you do with this board, maybe you could try a sound chip, since i've never seen a CPLD based custom sound chip for 65xx systems before

You can find it on Aliexpress for ~2-3 USD per—of course, with the usual caveat of buying things from Aliexpress (though I will say I haven't had much trouble with them at all).

The 3.3V supply does present a bit of a problem, but I suspect that would apply to most CPLDs/FPGAs of decent capabilities; I'm going to try interfacing to my SBC through a TX0608e, but I'm also noodling with switching over my design to 3.3V just to see what the tradeoffs are in practice.

Very cool! I really wanted to implement a tilemap, but I just couldn't figure out how to fit it in the available space, so I made a different set of compromises. That's definitely in the to-do list for my next design, though… when I eventually get to it

Yes, that is an intriguing thought, though I wonder whether having to serialize everything would end up affecting performance too much. My design also only needs unidirectional level shifting, which does simplify things a little bit.

Thanks for the font! I will give it a go. I'm still a bit unsure about what to do for sound, TBH—I've been putting that off till the end while I was trying to figure out the rest, and video seemed like a harder nut to crack (and it was… I've been trying to build a video interface using discrete logic for months!). My current thinking is to use some kind of MCU; there are some from Microchip that come with dual DACs and enough memory to make a synthesizer possible. With a CPLD, I would be worried about having enough room to store wavetables, though the MAX II does come with 1kiB of flash RAM, so it might work in the end.

Another thing I want to play with is replacing the 50MHz oscillator on that board with a 100MHz one to see if it still works reliably. That would double the number of memory accesses that can be performed in between pixels, thus opening up some interesting possibilities.

Cheers!

hmm, i have never used Aliexpress before, and seeing all the horror stories of the quality of products i'm rather hesitant to try it, plus since it's an SMT package you can only really test the ICs after you soldered them onto a board, which does make it more risky.

running a whole SBC at 3.3V shouldn't be much of an issue, the 65C02/816 can likely run at 16MHz at 3.3V, and 3.3V SRAM/FLASH is insanely cheap.
for example you can get 10ns 32kB SRAM for like 1.30 EUR/USD on Mouser, and 70ns 128kB FLASH for 1.20 EUR/USD.
downside is that you'll have to solder SMT when dealing with 3.3V Systems as not everything is aviaible in socket-able packages like PLCC or DIP.

honestly when i made my version i did kinda cheat.
I'm using a Logic Simulator called Digital to design and test the VGA circuit (it has a very accurate built-in VGA component) and when i'm done i just go to file -> export to Verilog, and then import that into Quartus II.
it has worked perfectly so far, but it also means i'm probably wasting some performance/logic compared to just writing Verilog myself.

specifically i've been thinking of using these IO Expanders to connect any kind of 8-bit Parallel peripheral via SPI, though something like a sound chip seems like a better idea as that doesn't need a lot of bandwidth compared to a video circuit that could require updating the whole screen 60 times per second or more.
it would still be an interesting idea because then you could also hook it up to a Microcontroller, just imagine an Arduino with good video output that doesn't stress the MCU!

100MHz for 640x480 would give you 4 Memory cycles for each pixel. in theory that allows for 32-bit color per pixel. seems a bit overkill though.

my VGA controllers both run at 25MHz and access Memory at 12.5MHz. the bitmap one needs 1 memory cycle every 8 pixels (or 16 cycles), the tilemap one needs 3 memory cycles per 8 pixels (or 16 cycles).
if you want to you can check out my Tile based VGA Circuit:

but be warned that even i barely know what is happening in there, so it might not be that useful.
but if you want to try out Digital for yourself maybe you can make use of it (the SNYC circuit is pretty solid and can be used for something else)

Very Cool!

Max II has up to 1K of internal flash memory which can serve as bootstrap ROM so you can boot from Max II then load application program from CF or SD. It is possible to build a very simple 3.3V standalone 6502 system consists of 6502, Max II, system RAM, video RAM, SD/CF and PS2 keyboard.

PS, if you design in schematic you can squeeze even more functions into Max II.

Interesting. I'm using the Xilinx xc95288xl CPLD for exactly such a system in my MicroPET design, but it costs way more than $10. On the other hand it's 5V tolerant which helps with attaching 5V IO (Commodore PET compatible), without the need of voltage converters between cpu/ram/cpld and IO.