First, a little background.
About a month ago, Rich Dreher tipped me off to an EEPROM issue he had seen in the past when interfacing an EEPROM to the Apple II bus. Well I didn’t have any issues with my prototype unit, but decided to do some additional testing with different EEPROMs. Back in the lab this EEPROM testing got confused with a flakey motherboard issue and the whole thing set me back a month.
After moving to a different motherboard, I eventually figured out that ATMEL EEPROMs don’t play well with the Apple II address bus, just like Rich indicated. However, an alternate source, XICOR, makes EEPROMs that do seem to behave quite well, so I’m back on track. During initial bringup, I had done my original testing with XICOR, which is why I didn’t see the problem with ATMEL parts.
So besides checking out EEPROM behavior, I made some design tweaks, checked out bus timing, made sure interrupts work and so on. At this point everything looks good,so I just pulled the trigger on a small trial run of boards. With any luck I may even manage to get some sent out to those of you HW hackers that are visiting K-Fest.
I plan on completely documenting this board including the GAL online, so little to no printed documentation will be created. If I can figure out how to do it, I want to set up a wiki type documentation environment where prototypers can add their own designs and share their knowledge with everyone else.
Here is the top side layout:
The base feature set includes
The hope is that this board takes care of all the heavy lifting of interfacing to the Apple II bus and lets you focus on the the fun side of hardware hacking on the Apple II.
Pricing hasn’t been set, but it will be well under $100 for a kit. Bare boards will also be available.