6502 Processor

[jllancee]

Hi, I am an undergraduate student who is working on making a model of 6502 processor in Digital software. This is based on a 6502 Logism file 6502.circ (see google drive link). I am getting an error when starting the simulation in Digital (photo attached). Files are inside the google drive link. Does anyone have a workaround for this? Appreciate your help. Thanks!
[https://drive.google.com/drive/folders/1Qx7kxJC0kgGlBitxH1MQk2_apWUsASB1?usp=sharing])

[mengstr]

I tried to run the main file and made a note of the statues of the wires leading into the ALU module. I then opened the ALU and ran it and setup the inputs the same as what the main was putting into it. It turns out that the Alu_add and ALU_AC modules both tries to output data on the SB_out bus. There are so many control signals that I can't wrap my head around everything, so I can't help you further. But at least you have something to work from.

[jllancee]

Thanks!

[logoliv]

@jllancee Could you please share your project on Github if it works ? I think many people would like to simulate a 6502 with Digital 😄

[completely-unstable]

i have one that can at least run fibonocci:

Untitled.mov

and it runs actual assembled machine code:

but im still working on getting all the instructions implemented correctly. also how would i upload to github, do i just need to include every dependency?

[SirClickALot]

I strongly second that!
@jllancee please do share it, it would be very useful indeed.

[shawty]

I started writing a 6502 & 6522 simulation for Digital using the Java Components extension point, log time ago... then work got in the way, and nothing ever got finished.

Just had a quick look, I thought I'd actually uploaded them to my github page, but if I remember correctly, I did actually raise something as a issue/help request on here in digital's early days.

Just had a poke about to try and find the thread, it turns out I had it in the "Custom Components" repo.

From the quick read I had, I think I didn't get much further than starting to implement the 6522.

You can find the thread here

hneemann/digitalCustomComponents#3

With zip files containing the Java code still intact and downloadable.

[completely-unstable]

@logoliv @SirClickALot https://github.com/completely-unstable/6502-Digital

[completely-unstable]

cool, ill check it out. i would really like to know what exactly are the control signals that get set each cycle, ive found the # of cycles but dont really know what happens during them.

[shawty]

@completely-unstable in most cases the 6502 is really a very simple step wise CPU.

If an instruction states it takes 2 clock cycles, then your most likely looking at an instruction decode followed by a load, 3 cycles usually an ins decode followed by a 2 byte operation of some kind, the only time it starts to get a bit tricky is with Zero page, and long addresses, Rodney Zaks book that I mentioned above will take you through everything like that, there is a wealth of information in the book.

[shawty]

@completely-unstable here we go. I knew I had this somewhere :-)

6502 Schematic.pdf

Enjoy.....

[hneemann]

@shawty
This schematic is amazing! Thank you very much for sharing!

[shawty]

@hneemann your more than welcome :-) I can't take credit for drawing it, but I have had it for a long time, I don't remember where it originally came from, but I suspect it was back in the day as a teenage programmer, writing off to electronics companies begging them for technical info when learning how to program the 6502 back in the 1980's.

That PDF is just a scan, somewhere (I do not know where) I will have the original document.