Working on the 65816 board
I have received the new board.
It looks great and is ready to go! I started gathering my parts (mis en place in chef speak), just to realize that I was a few pieces short. They’ve since been ordered, but it will be a few days before I can finish the board.
The current design is based on the Flex-ATX form factor. This will fit into any micro-ATX or larger case, and I’ve left the rear I/O backplane marked off. It’s totally unnecessary at this point, but I wanted to start with some good design practices in mind. It also includes the LCD still on the board, which will moved to a daughterboard eventually. The card slots I have no idea if they match up, because that wasn’t part of this design iteration. In the end it will have three, and where I have I/O header will be the third slot. Also there will be a cartridge port…. somewhere? And a keyboard interface? And a controller port? Ugh, let’s just get this thing working first!
I have all of the chips necessary, though mostly by pulling them from previous iterations of the 6502 board. Though that’s fine, as I only plan to keep the final version(s) populated in the end. The 6502 phase was for learning and following along with the Ben Eater series. This first draft of the board is not without it’s errors. I used the wrong footprint for the DIN41612 connectors, for one. There are a bunch of silkscreen errors that I’ve made, for another.
So being short some parts, I did keep track and write them down. I just ordered the sockets, as well as some ZIF versions as well. Also my notes on what was wrong (so far).
I didn’t even think about the size of the 128K RAM chip, obviously it needs more pins than a 32K chip. I don’t have any 32 pin sockets, so I ordered a few dozen, because they’re cheap and I will definitely go through them.
I need skinny 20 pin DIPs for the latches, and my kit of various pieces only had wide ones.
I’ve used so many 14 pin DIP sockets already that I just ordered another 100.
I couldn’t remember why I had 2 555 timers, and why one was a U designation and one was an IC designation… That’s because IC17 is actually the 10ms delay chip.
Getting down to business
Being short some parts, especially flat ones, I decided to get started anyway once I ordered what was missing. I put in all the sockets that I had, including the ZIF 28 pin one for the EEPROM. I put the 555 timer straight into the board, as I always do (because they’re cheap and plentiful). I did all the 103 capacitors that I’m using to smooth out the power for the ICs, and the larger filter cap at the power entry. I did install the headers for everything (except the delay lines, more on that later), and the barrel jack for the power connection. I’ve gone with a 5V center positive, as you can see in the silkscreen on the back of the board above.
Additionally, I decided not to place the 28 pin sockets for the video ram in this version, since they’re mostly just there to ensure I account for their space for now. It’s entirely possible that they will move to a daughter card as we go along, potentially for vertical mounting for the ATX case, or to be an internal expansion (and upgrade route) for the wedge case.
There are a large number of unpopulated headers throughout the board. These are the unused logic gates from any of the 74xx logic that exists on the board. I briefly contemplated doing the same with the programmable logic, but decided against it for now. Maybe in the next version if I find I need it.
Thanks to u/rehsd for the idea!
Parts laid out on the board prior to soldering.
The last little bit is the design calls for one of the 6522s to be hidden under the LCD for now. It does fit, but just barely.
