Hi 6502ers,

I'm going back to the drawing board with a rev 3 of my 6502 SBC. Rev 1, a larger board with expansion slots, only contained the CPU, ROM, RAM, and an ACIA; it also was designed to be breadboard friendly. I used it extensively for prototyping. Rev 2, on the other hand, was designed to be only 100mm x 100mm, contained all of the above plus an NVRAM. Rev 2 has daughter boards for peripherals such as VIAs and an MCU for mouse, keyboard, and NES controller, as well as a video card (TMS9918A), and a sound card (3x AY3-8910).

Having said that, Rev 2 is a pseudo flop. The main CPU board is flaky. There are several issues I have identified. Amongst them is the clock (if I leave my scope probe on the clock, my problems are 95% solved). I have posted my woes on the 6502 Facebook group. Many helped me out in identifying my issues. Oh, and one more thing about my woes! My crystals for the ATMEGA328P (Keyboard and mouse controller) and the TMS9918A (VDP) won't oscillate (I have changed my capacitors for different values, just in case). Though I did notice my voltage was at 4.89V (caused by a cheap slide switch, acting as a power switch). All in all, it's time for a redesign. I shall re-read Garth's Primer for sure. And if you have links to design ideas, feel free to post them my way.

- I shall have one big board (instead of expansion or daughter boards)... well probably one mezzanine board if all of the above won't fit.
- WD6502 running at 2MHz (4MHz through a 7474 FF to have a clean strong clock) (some of my components won't support higher speeds)
- 32K ROM, 32K RAM
- Still debating between staying with Atmel ATF22V10 for glue logic, or going all-in with conventional jellybean logic. And which family would serve me better? I have a few F ones (very fast)
- I'll have an MCU to interface the PS/2 keyboard and mouse (as well as an NES controller)
- 4 Rockwell ACIAs: one DTE, one DCE, one for HMI display, and one for future expansion
- 4 VIAs: One for MCU interfacing, one for SPI-10 ports, and 2 others for future expansion
- 1 TMS9919A or TMS9928A (I have both in multiple copies)
- 2 or 3 AY3-8910 (Stereo, or Stereo+center) (I have multiple copies, so I'm tempted to put more
- I'll have to find a RTC
- Still debating to put an LCD since I'll have terminal access, and a VDP

Sounds ambitious, but all of the above (except the RTC) worked on a breadboard prior to the failed Rev 2 experiment.

Do you have any suggestions, ideas, changes, critiques?

_________________
Fred Segard
A.K.A. The Micro Hobbyist
https://6502sbc.blogspot.com/

I have finished my schematics for my 6502 computer. Any do's and dont's, advice, ideas, and/or critiques are welcome.

PS: I realize I forgot to put the 40x4 LCD. But then, since I have a VDP, it might not really be necessary.

_________________
Fred Segard
A.K.A. The Micro Hobbyist
https://6502sbc.blogspot.com/

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

I'd be glad to help. But, honestly, I find it too laborious reading a schematic like this. Maybe that's a valid critique and maybe it isn't; I'm only speaking for myself.

Oh -- and for BigEd, too, who recently opined, "But the kinds of schematics which just show a field of isolated components with all the connections as stubs isn't, to my eyes, as good as one which follows a logical block diagram."

Yes the information is all there. And some questions are easy to answer, like, "regarding IC pin blah-blah, what signal does that connect to?" But not so much when you turn the question around and want to know, "regarding signal so-and-so, what IC pins does that that connect to?"

(Oops, I see Garth has posted while I was typing. Like him, I hope you don't take this as condemning.)

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Valid point. I'll be careful in my designs next time.
Oh! Yes, I see the error of my ways on this. Thanks.

_________________
Fred Segard
A.K.A. The Micro Hobbyist
https://6502sbc.blogspot.com/

Not at all, I just learned something quite valuable in schematic design today. I will do better next time.

_________________
Fred Segard
A.K.A. The Micro Hobbyist
https://6502sbc.blogspot.com/

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

Thank you for the example. I shall use it as inspiration when I redraw mine.

_________________
Fred Segard
A.K.A. The Micro Hobbyist
https://6502sbc.blogspot.com/

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

I've just tried the pre-Autodesk version of Eagle that I'm sticking with, and it does. When you print, there's an option for "page limit". It will automatically scale down the schematic until it fits on that number of pages. With it set to 1, everything gets squashed onto a single page. Set it to 1000, and it will take as many pages as it needs.
I expect that all of the others (the ones intended for professional use, at least) will do it too. But I don't have any experience with them.

Standard engineering drawings (Size B/C/D/E) are multiple of 8-1/2x11 so if you think ahead and place a large design into half or quarter groupings, you can print them out in half or quarter and tape them back together without splitting components or signals.

I think B-size (11x17) printers are still economical so D size or even E size drawings can be stitched together and be perfectly readable.
Bill

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

I fondly remember my days designing on large lighted drafting table with data books and sketches spreading all over the table. It was a pleasant, creative environment.

I also remembered "discovering" electric eraser, wow, that was a game changer! We were easy to please in those days.
Bill

With KiCad, you can co up to E size (34" x 44"), and even customize your size. I'm sure most programs can do this though. But I'll have to try to see if KiCad can segment into 8.5" x 11x sheets.

Would a single large schematic be preferable when posting?

_________________
Fred Segard
A.K.A. The Micro Hobbyist
https://6502sbc.blogspot.com/

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?