Bluemeanie's Retro Computing

I needed to change a minor detail in hardware design to make the card work and I was happy to hear that some of you folks have made their own PCBs from my design. Here are the changes that are needed to make the current ROM and CPLD work with a V1.0 card: On the front: Remove resistor R10 and make a connection between the left pad and pin 13 (A11) On the back: Cut the trace between pin 30 (/IRQ) and the via.

Last night I had a major breakthrough for my SD card interface! Not only does it work, it boots GS/OS on the Apple IIgs! 🎉 Switching the source code from Merlin-8 on the IIe to CC65 in Visual Studio and using an EEPROM sped up my development cycle quite a bit. This wasn't a fix for the issues, of course, but it helped. As usual, there were a lot of small things involved and I have learned some lessons. First lesson: the disk status function uses the X- and Y-registers as return values. However, when you load these registers with the return values and then insert a function call that does not only save these registers but uses them for slot addressing, it will crash. There simply isn't a slot number 255 in the Apple II 😉 Second lesson: SDHC cards use block addressing, not byte addressing. Some weeks ago, my 512 MB card died and I replaced it with an 8 GB card. I knew before that it was initialized correctly, so I assumed it worked as well. The problem was b...

It has been quite a long time since I had some spare time to work on my still-not-working SD card interface for the Apple II. After rewriting almost all of the VHDL code for the card's CPLD it still would not boot and most of the time crashed with a more ore less garbled message of "Unable to load ProDOS". The fact that this message is shown at all means that at least the first block of the volume is loaded and executed. But the messed up message indicates an issue in the transmission either from card to CPLD or from CPLD to the computer. I checked the data coming from the card and it seems fine. Thanks to Protek over at the Applefritter forum, I found a step into the right direction. He built a card from my design and uses a quite old version of my sources, that was sort of working. He swapped the 74HCT type bus transceiver for a 74LS type and instantly got better results. I tried the same and got better results, too. Well sort of. The "Unable to load ProDOS...

So, my first participation in a RetroChallenge was some kind of a failure. Apart from a very basic prototype I have not achieved my goal in building a replacement for the Apple II Mouse Card at all. Instead I got distracted by my other project, the SD based mass storage. Since I wanted to use the same CPLD based design I figured I'd get that one right first. But after having changed almost everything, it still does not work and I'm kind of out of ideas what else to do. But like the Olympics, it's all about being part of it. Maybe I'll have more luck next time.