Sunday, December 30, 2012

Retro Research

I took some time this weekend to get a jump on the Retrochallenge. As the Disk ][ emulator will be my first hardware build from the ground up using standard digital logic integrated circuits, I have been doing a lot of research and note taking. Copying or just assembling an existing circuit can be hard enough on in its own. Learning a new (for me) technology (even if it is excruciatingly well documented) takes a lot of time and preparation.

As Sun Tzu said:
To rely on rustics and not prepare is the greatest of crimes; to be prepared beforehand for any contingency is the greatest of virtues.
Speaking of "rustics":

Rusty IIgs Horror Show!Reading Material
Oddly enough, my automotive bodywork skills may come in handy here.

I can't encourage any electronics experimenter enough to get one of these data books. These cost me $1 a piece at my local surplus store. Sure the data-sheets for all of these ICs are online, but it is so much easier turning a page than searching, finding and opening the right PDF, saving it, closing the pop-up ads...

Monday, December 24, 2012

Another Challenge

Add another challenge for me.  Since I expect to be working on both my Apple IIs to fix them up, I wanted to get one that I could just work on to develop the disk emulator project. I picked up a Apple IIe platinum from a guy on craigslist who is developing an app to "reinvent classified listings." It looks like it is in decent shape, but is very dusty and is missing a few keys. Hopefully, it will be easy to get it clean and running.

Apple IIe Platinum    dusty Apple

Wednesday, December 12, 2012

Virtual Disk Research

To prepare for my Retrochallenge project to build an Apple Disk ][ emulator, I have been researching some 'prior art' on the subject. Here are some of my favorites:

Pseudo Disk ][ Controller Card
Nice project. The megaAVR I can handle, the Xilinx CPLD puts this over my head.

SDISK II - DISK II emulator for APPLE II (or version 1)
Cool, and accessible. The device uses a megaAVR, but uses the the standard Disk ][ drive controller card. This is great because it potentially allows an Apple //c without slots to get in on the fun using the built in drive controller (but no slots). It appears to use the same, or similar, megaAVR code as the Pseudo Disk ][ Controller, above. This design appears to have a hard time keeping up with the bandwidth required based on the over-clocking that is necessary. I don't like the use of non-standard disk images either.

Semi-Virtual Diskette (SVD)
Uses SRAM instead of SD card. Requires special PC only software.

Nice looking product. Compact Flash. Requires a slot. Not DIY.

Smartport Virtual Hard Drive
This looks very doable. Unfortunately, I don't have a SmartPort based computer! My Apple //c only has the original version 255 ROMS. I like the use of commodity hardware, but the Micropendous board runs about $60. Certainly affordable, but I am trying for cheaper.

HxC Floppy emulators
Very nice! - if you have any type of computer except an Apple.

Macintosh Floppy Emu
Whoa! Very cool. Maybe one day... Macintosh only. not DIY.

So, I am going for something like the SDISK II, but I want to use strictly SPI to make the transfers to the Disk ][ controller card. Based on my reads of "Understanding the Apple II" (82Mb PDF book download), I think I can multiplex all of the Disk ][ signals into an SPI standard stream. This should free up some processing power on a micro-controller with native SPI, and should free up some pins for an interface to select the active disk image.

Saturday, December 8, 2012

Retrochallenge 2013WW

I just noticed the call to arms for the Retrochallenge 2013 Winter Warmup. I tried to enter in the past, with no luck. In fact, I never got around to even starting that project. Since then, my interests have moved from early Apple Macintoshes to Apple II's. So my projects for the Retrochallenge 2013 Winter Warmup are as follows:

Apple II Disk Emulator
Unfortunately, 5 1/4 inch floppy disks are hard to come by these days if you want to play around with online disk images. ADT is a great project that I have used with some success in the past, but for the most part, you need disks or live connection to another computer. Other projects, including one created during a previous Retrochallenge, require a connection to another computer and cannot use disk images. I would like to build an SD card based virtual disk drive for an Apple II using standard commodity hardware you can find on ebay. There are some projects out there, but none do exactly what I want. I have an idea for converting the Disk II signal to SPI to read it from a microcontroller or an FTDI serial UART.

Apple IIgs Upgrade Restoration
I used to own a pristine Apple IIgs upgrade with original version 00 ROMS. I still own it but it is no longer pristine. The clock battery inside the computer exploded several years ago, causing serious damage to the logic board and rust on the case and power supply. My plan is to get a new logic board and repair the rust damage, restoring the IIgs to working condition.

Apple //c ROM Upgrade
I have an Apple //c with original version 255 ROMs. I just bought some AT29C256 EEPROMs from ebay which appear to be compatible with the Apple ROMs. My hope is to get an updated ROM image onto one of them somehow. I own a Mac and I don't own a ROM writer, so I am hoping I can get a simple ROM writer made with some standard ICs. A few counters to increment the address and a shift register to shift in the data from my FTDI UM232H should do the trick.

Fortunately, work is pretty slow in early January, so I think I can get at least one of these projects completed.