Hi, all - just wanted to introduce myself. I recently became enamored with the 65c02 and it’s ilk, and I’ve been experimenting with the WDC chips now for several months. And, yes, I’ve been reading (but not trolling!) this forum with great interest. David G from WDC has been extremely helpful with getting me started, pointing me in the right direction (here), and I’ve really learned a lot from these fora.

Amongst other things, I’m working on implementing my first soft 65c02, and I’m using the Arlet 65c02 verilog model. I’m sure these are dumb questions but, here I go: regarding the reset, irq, nmi, and write enable signals... am I wrong to believe that the logic is inverted here? In other words, are reset, irq, nmi, and WE active POSITIVE signals in Arlet’s core? I’m slightly confused, especially regarding something so basic. I’m using the Digilent Cmod A7 and Cmod S7 to do this, so I have proper SRAM. Is it possible to use real async SRAM Witt Arlet’s 65c02 core?

Any help you guys can offer here would be greatly appreciated!

Jonathan

Welcome Jonathan!

Without making a definitive statement, I'd say it's quite possible that Arlet has chosen to use positive sense signals, for convenience or clarity or personal preference. As it's an open source core, that would be extremely easy to adjust. In fact I think it's common enough to make these adjustments at the interface, as you instantiate the core. You might be interested to look around here:
https://github.com/hoglet67/CoPro6502/b ... t.vhd#L180

And yes, I'm sure you can use async SRAM with Arlet's core. Again, you need a shim, or to make an adjustment, because the address and control signals will need to be presented in the same cycle that the data is captured, rather than the previous cycle. So, yes, but you need to do a little work.

Ed,

Thanks. I'm a verilog guy, but I get it - the author inverted the reset (RSTn_sync) and Write Enable (cpu_we_next) signals.

As an aside, I'm glad to hear from you, in particular. I've read many of your posts. However, looking at the (old) dates on many of the posts I've perused, I was deeply concerned that I'd come to the party way, WAY, too late to interact with anyone. I'm glad that's not the case. It seems that the 65xx ICs are alive and well in 2021.

Jonathan

Never too late to the 6502 party!

There is a huge amount of previously posted material by now - even when I joined, there was a lot, and although I did read some backlog, I think I have not read everything.

Garth's primer is frequently mentioned, and rightly so, so do search for that and have a read.

And it's fine to resurrect old threads, if you are continuing the conversation. If going off on a tangent or a fork, make a new thread but link back to previous findings if you can.

Ed,

Thanks! Funny, but Garth's primer is the first "document," or guide, I read. I had the idea/desire to learn how computers actually worked, so it seemed natural to read up on how to build a 6502-based machine. I read Garth's "instructions," I watched some of Ben Eater's videos, and the rest is history. I've really gotten into it , now, so I wanted to join the conversation - and I'm glad that there IS a conversation. Plus, everyone has been friendly and helpful; I was pleasantly surprised when I got emails from names I recognized at WDC, etc., answering the questions I, a newbie, had. Now ... my dining room table is my engineering station (and it's Spring-Summer, so my family can eat outside). Kidding - sort of. This stuff is very addictive; I have a lot of ideas I want to try out.

Jonathan

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

Precisely. When I initially decided to purchase 65xx ICs, I was surprised how readily available they were - I really thought, in 2021, it would be a chore. I was wrong - they are everywhere. The 'c02, VIAs, ACIAs, even PIAs - easy. The only chip that was a little more scarce was the 'c816 - and by "scarce," I mean I could only find it at Mouser, but, even there, the stock is plentiful, so I grabbed two. The very first item I got, though, was the 'c02sxb, to learn how to start programming in assembly. A reference platform. However, there wasn't really much out there, discussion or code, specifically for that single board computer. That was a little surprising.

With the help of WDC, I also obtained a soft-core mensch rev-c (with the headers ON) - along with a brand-new break-out board they just released for it, the "MyMensch PRO Board". A brand new 65xx product in 2021 - mind boggling (that there is a new, contemporary, device based on a technology designed in the '70s). I don't know if you guys have seen it, but it is begging to be tinkered with by the experts.

Right now, I'm trying to get Arlet's 65c02 working on my cmods, but it's still outputting garbage. I'm using the "generic" core - I don't have a Spartan-6. What is throwing me somewhat is that there are two "ctrl.v" files - one in the main "generic" directory, one in its own folder (a larger file). There is no instruction as to which to use. The only difference is that the larger file doesn't seem to incorporate the microcode. Like I said initially, any help would be appreciated. I've also tried every setting for reset, irq, nmi, and rdy. Nada.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

Agreed. I obtained my “MyMensch” parts directly from WDC (the FPGA stuff), and everything else is from Mouser or Jameco (but, mostly Mouser). (Un)shockingly, everyone I’ve dealt with at WDC, Mouser, and Jameco has been nice, pleasant, and extremely helpful. For example, Mouser had a big problem when Texas was hit with disaster a few months back, but they still managed to organize and ship out my order next-day, as promised upon my purchase. David Gray at WDC has been EXCEPTIONALLY helpful - he’s helping me, as needed, on an ongoing basis, helped me get my FPGA stuff from WDC (headers and all!) and even took it upon himself to ship it. Now THAT is extraordinary. He's sort of my 65xx Sherpa . So, yeah, in short - lol - I am following your advice and only dealing with trusted sources.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

I need to look into that; my EEPROMs are AT28C256 knock-offs from Amazon. Crapola. Slow as molasses. I need to find some good, fast, reliable replacements.

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

I use a work-around... For testing, I've been using a small monitor with an x-modem based bootloader to load .prg files into "high" ram - I've been mapping a low RAM from $00-$7FFF and a high RAM from $9000 - $E000. Small ROM from $E000-$FFFF and lots of decoding between $8000-$9000 for the peripherals. I'm really just learning the basics, so that is more than ample. For assembling, I've been using VS with Retro Assembler. No particular reason - I'm just comfortable with it.