Hardware Revision 4: Now with All the Pins You Need!

A project log for L-Star: Software-Defined 6502 Computer

Replicate an Apple-1. Or an OSI Challenger. Or something else. Design your own 6502 computer by programming it.

jac-goudsmitJac Goudsmit 08/28/2016 at 22:080 Comments

This weekend I was able to do some work on the hardware of the project again, and I decided to bump the version number, so it is with pride and joy that I announce Revision 4 of the L-Star hardware.

One change that I made since Rev. 3 (which I never built) is that the PCB is now even smaller. It's now within a hair of fitting within the "magical" 80x100mm "Half Eurocard" size. The short side is 0.01mm too wide to fit into the crazy limit imposed by the free and cheap versions of Eagle. I don't think I'll fix that unless someone asks; I think this design is going to be the production version.

The most important improvement compared to revision 3 is that the expansion port is now a 50-pin header instead of a 40-pin header. As I mentioned in the previous project log, the location of the expansion port was always designed with the possibility that there could be a 50 pin header some day, and that day is now. For most projects, the original 40 pins may be enough, but the extra pins should remove any fears of future regrets: Simply every single important control signal is on the connector. The added pins are:

There are actual people owning actual hardware that uses the 40 pin connector, so the 50-pin connector is backwards compatible with the 40-pin connector. The two GND pins were added on one side and the 8 other pins were added on the other side. I don't expect to make any further changes to the pinout, because all the signals that I think could possibly interesting to any expansion devices, are on the connector. The only ones that are not on there are the Propeller clock and the brown-out protection. But I already decided that it's not worth making any changes to those: the project is intended for those who want to learn about the 6502, and while those two would useful, they would also be a distraction from the intentions of the project and add expense.

I ordered a batch of PCB's from OSHPark, and I plan to build it to make sure it works, I'm thinking of leaving the chips off the Mouser order, and stocking up on the passive components so I can do a production run soon, and finally put the project up on Tindie.