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Re: The J64C (version 0)
Posted: Mon Jul 19, 2021 2:40 am
by J64C
That’s the thing, the manuals seem inconsistent. When you look at the W65C02 manual it states, 14MHz at 5V. Then you look at the graph and it does show ~25MHz at 5V. Then even ~40MHz at approx 7V.
Welcome to the wacky world of WDC documentation. Especially in their older data sheets, there are quite a few errors. Fortunately, their products are much better than the data sheets would lead you to believe.
Nice! I noticed even the max voltage ratings were all over the place too. Early pages suggesting it can run ‘up to’ 5V (+/- 5%). Then later on 7V.
It is fantastic, though, that WDC have kept the 6502 alive and kicking.
Re: The J64C (version 0)
Posted: Mon Jul 19, 2021 2:42 am
by BigDumbDinosaur
That’s the thing, the manuals seem inconsistent. When you look at the W65C02 manual it states, 14MHz at 5V
That's the conservative guarantee, to do at least 14. It may (and does) go faster, but it's just not guaranteed to. Forum member "Windfall"
has a 65816 running at 24MHz at 3.3V! That's three times the 8MHz it's guaranteed to do at 3.3V.
What is confusing is the FMAX vs. VDD curve for both MPUs suggests the performance is substantially better than what the timing data would lead one to believe. The curve seems to have been revised at least once, as I recall, and that revision seemed to occur not too long after the geometry was shrunk from 0.8µ to 0.6µ. I'm suspecting the curve was revised to agree with the better performance that could be expected from a 0.6µ core.
Re: The J64C (version 0)
Posted: Mon Jul 19, 2021 2:44 am
by BigDumbDinosaur
It is fantastic, though, that WDC have kept the 6502 alive and kicking.
You have no idea. 
It is estimated more than 100 million devices containing the 65C02 or the 65C02 RTL in an ASIC are produced annually.
Re: The J64C (version 0)
Posted: Fri Jul 23, 2021 1:01 pm
by J64C
Planning to get back into this over the weekend (which is in about 10 hours here). Wish me luck! Haha!
Re: The J64C (version 0)
Posted: Mon Jul 26, 2021 7:30 am
by J64C
Haven't done much with this in a little bit, but finally felt like chipping away at it today. Refined things a little this afternoon.
I came to the realisation that I make my connections 'semi loosely' standard, so I was able to ditch the cabling between the RAM board (which also acts as the systems ROM) and dump the board directly on top of my CPU board. Guarantees no bad connections and should have a much cleaner signal.
The ribbon cable you do see there is just going to my homebrew logic analyser. Later on I can just unplug that part of it entirely.
I'm still not qualifying my writes here, so that's next. A lot less visual noise to mess with now, so I'll be in a better mindset for it.
Re: The J64C (version 0)
Posted: Wed Jul 28, 2021 2:55 am
by ThePhysicist
Is that a lego baseplate?
Re: The J64C (version 0)
Posted: Wed Jul 28, 2021 8:12 am
by J64C
Is that a lego baseplate?
Haha! Yes it is. Best prototyping gear there is!
Re: The J64C (version 0)
Posted: Wed Jul 28, 2021 8:24 am
by J64C
Started re-attaching my video card boards bit by bit to this project today. It has a 25.175 oscillator can, which I have going through a clock divider which allows easy access to clocks down to 1.5MHz. So did a bit of testing.
1.5 MHz - Works! Cool.
3.125 MHz - Still works. Nice!
6.25 MHz - Yep! Great!
12.5 MHz - Which is my target clock rate. Stable! Awesome!
Hmmm. Do I dare 25 MHz? Of course! Haha!
25 MHz - Running stable for the past hour! Freaking awesome!!!
Still wring the video card up bit by bit, testing as I go. But I am super happy with the progress going on here.
Re: The J64C (version 0)
Posted: Wed Jul 28, 2021 10:43 am
by BigEd
Excellent!
Re: The J64C (version 0)
Posted: Wed Oct 27, 2021 2:14 am
by J64C
Been a while since I worked on this. So I started getting my head around where I was at.
Did some fine tuning on the graphics board today and am very pleased with the progress. Still as of yet to get to the point where my CPU talks to it though. One step at a time!
I'm probably going to move straight on to using a W65C816 as memory requirements of my graphics board is an issue (unless I crush the resolution, which I don't really want to do).