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  • Writer's picturerehsd

65816 "PC" PCB Progress

Updated: Mar 13, 2022

I have the initial layout and routing working for my 65816 motherboard, video card (including memory daughter boards), and prototyping add-in card. In the coming week, I have plenty to do to get these ready for production:

  • Final addition of components.

    • Bus resistors on motherboard.

    • Add any missing filtering caps.

    • ISA slot pin headers on motherboard (for tapping into add-in card signals from the motherboard).

    • ...whatever else I find that I'm missing as I scrub it.

  • Final tweaking of component locations (e.g., alignment, spacing, best footprints).

  • Adjustment of all labels (e.g., position, rotation).

  • Validate every connection. This is going to take a lot of time.

  • Switch all boards to four-layer. I've been waiting on this, as EasyEDA still struggles with four-layer boards that have inner planes (as of the 12 March 2022 release, version 6.5.1).

  • Validate physical fitment of motherboard, add-in cards, and daughter boards. This includes double-checking motherboard dimensions so that it will fit in an ATX case.

  • Add silk-screen information to identify ICs, resistor sizes, functional areas, pin header details, etc.

This is what I have right now:

Here's the pinout I am using for the ISA slot:


Postscript

As I get closer to ordering, and as I "complete" each piece, I'll post details below as I go. I plan to use JLCPCB for production, and I'll include per board estimated pricing.


Total estimated cost for PCBs for a single system (i.e., one of each PCB, with the exception of two VGA daughter cards): $56 USD. Since I must order a minimum quantity of five of each PCB, the resulting order will be approximately $250 plus shipping. Well, there goes my fun money for a while!


Expansion Proto Card

Four-layer "breadboard" that can interface via ISA connection to my system.

Price per board: ~$12 USD.

Schematic Proto Board 20220312
.pdf
Download PDF • 162KB

VGA Card

Four-layer board for 320x240x1B (RRRGGGBB). Requires at least one VRAM daughter card.

Price per board: ~$11 USD.

Schematic VGA 20220312
.pdf
Download PDF • 409KB

VGA Daughter Card (Stackable VRAM)

Four-layer, stackable video RAM board. The video card can support a total of four stacked daughter cards, with each card holding two dual-port 32Kx8 SRAMs. (I intend to use half of that -- 128Kx8).

Price per board: ~$8 USD.

Schematic VGA Daughter Card 20220312
.pdf
Download PDF • 260KB

65816 Motherboard

Four-layer 65816 motherboard.

Price per board: ~$17 USD.

Schematic 65816 Motherboard 20220312
.pdf
Download PDF • 1.00MB




A Late Addition

I figured I better have an LCD option for the system. I put together this little PCB that will let me connect it to an ISA slot and connect an LCD with a right-angle pin header. This way, the LCD will face out from the ISA slots. I added some room for general use needs, too, such as pin headers and an empty spot for an IC. I could connect LED bar graphs or other I/O.

Schematic VIA LCD 20220313
.pdf
Download PDF • 182KB


PPS

As I reviewed as many details as possible in the above PCBs, I did find a few issues that I have corrected. For example, I was missing an address line on my VGA to daughter card connection. I have also made some minor physical adjustments, based on bracket requirements. Once I receive the PCBs and fire them up, I will update schematics to correct any remaining errors (hopefully, none are too serious). I plan to post a summary of my experience getting the boards running and how much bodge wire I use. 😏 More to come in a few weeks!


PPPS

I wasn't liking some of the design issues I was having with the expansion proto board, so I refactored it. I can now use a pair of BB830's on the card, with easy access to all signals on the ISA bus, along with easy access to power. With this setup, I didn't think a four-layer PCB made sense, so I went with a two-layer design and increased trace width for VCC and GND.


Boards have been ordered! :)


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15 Comments


Thomas Mottl
Thomas Mottl
Mar 12, 2022

This looks awesome. I've been struggling with my 816 board design, but I've gotten a lot of inspiration from seeing how yours is coming along!

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rehsd
rehsd
Mar 13, 2022
Replying to

I use the two inner layers as VCC and GND planes. I could go for two-layer, but I like the idea of power distribution and noise reduction with the inner VCC/GND.

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Joe Plocki
Joe Plocki
Mar 12, 2022

For validating physical fitment, a buddy of mine once suggested printing the top layer at 100% scale, and laying components on it, and/or making sure it lines up. That's probably less headache than measuring and stuff.

Dang, 3 comments in 5 minutes, your site's going to ban me for spamming...sorry, rambly this morning.

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rehsd
rehsd
Mar 12, 2022
Replying to

My plan is to do a little bit of both. I will start with printing everything at 100% and verifying components falls into place. On my 65816 dev board I built a while b ack, the basic RAM had the wrong footprint (wide vs. narrow), hence the ZIF socket on the RAM, lol. I will also do a bunch of measuring in the EasyEDA toolset (which I have already done a fair amount of).


I appreciate all the thoughts and suggestions, Joe! Thanks!

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Joe Plocki
Joe Plocki
Mar 12, 2022

Oh, and I'm sure you're on top of it - but don't forget to remove the board area between the long and short sides of the edge connector for the ISA socket - that would suck to have that divider in the socket with no recess in the connector.

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Joe Plocki
Joe Plocki
Mar 13, 2022
Replying to

Awesome! Exciting stuff!

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Joe Plocki
Joe Plocki
Mar 12, 2022

On your proto-board how are you connecting the components to the edge connector? Do you have traces for specific pins to the prototyping area rows? Are you mimicking the ISA bus, or did you roll your own?


I'm working on something similar (I'm still very tempted by your ISA socket link, since my fingerboard sockets are only 40-position and 50-position, and 50 isn't enough if I also include enable signals and the "unused" '816 pins, and using both side by side seems like unnecessary headache, even though it would provide keying to prevent incorrect insertion).


I'm working on my next try at the 816 right now, using yours and the WDC 65C816SBX schematics as a reference while breaking out /OE…

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Joe Plocki
Joe Plocki
Mar 13, 2022
Replying to

Oh yeah... the "game" part is why I won't quit on VGA until I have sprites and tiles. Best math I can come up with, I'm looking at something like 10fps in the best case with bitmap graphics (which I'll support, but I need sprites and tiles). In fact, I'd like to port something like Super Mario World (unofficially and on the down-low, of course) to see if my hardware can semi-hang with the SNES.

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