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:
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.
Four-layer board for 320x240x1B (RRRGGGBB). Requires at least one VRAM daughter card.
Price per board: ~$11 USD.
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.
Four-layer 65816 motherboard.
Price per board: ~$17 USD.
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.
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!
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.