Apple-1 on FPGA

 I started with electronics in 1979 at age of 14. And am doing it ever since. One chip I really wanted to use was MC6809. I was even able to buy it on the black market. But I have never worked with it. But look what I did see today:

I see the welcome screen of Replica-1 compatible computer running on MC6809 compatible IP Core. My first ever greeting from 6809! Makes me smile.

HOW? Easy, I did take the existing Replica-1 repo at github here and then adapted it for the FPGA board on my table. What was on my table? It was AXE5-Falcon PCB with serial number #0. There is some info about AXE5-Falcon here.

I spent about two hours to get it to work. Why so long? Because the usual suspect UART RXD and TXD. They are swapped at the level shifter. So I did not notice that at first, so I swapped RXD/TXD several times with no luck. And then I realized that the FTDI UART pins at FPGA are in 1.8V bank, I had selected 3.3! That was the mistake and real reason for two hours debug session.

So now it works.

But I have no idea what I can do with it :) there should be possible to enable ROM BASIC, I so assume. And with PMOD SD card adapter it could even access SD cards?

Well, it works :) so I can ask the author what I can do with it.

It it is named as Replica-1, but Replica-1 is replica of Apple-1 home computer. So I have a Apple-1 on my desk.

UPDATE: by changing two lines of code the processor is changed to 6502 and ROM to Basic+monitor, with a magic:

E000R

The Basic starts, and it is possible to enter and execute Basic programs.

How big is it? On the AXE5-Falcon board, the logic utilization is less than 1%. For 48Kbyte RAM and 8KB Basic ROM, the block RAM utilization is below 8%. So I could instantiate 10 Apple-1 computers in a single FPGA!

What about really small FPGA? Trying out special version for MAX1000 with 10M08 FPGA. And here is an adventure game starting:

Note for UART downloading, you need to use teraterm (and not putty) and set line end delay to 7ms then the download works.