Floppy Emu on the Apple III
The poor sad Apple III never gets much love. It wasn’t popular in its time, and had a short lifespan, but today it’s a sought after collector’s item. My Floppy Emu disk emulator for vintage Apple computers supports just about every machine Apple ever made except the Apple III – or does it? The enterprising Patrick Longinotti reports his success using the Floppy Emu to boot and run his Apple III system, using a custom cable and the stock Apple II firmware on the Emu.
How is this possible? The Apple III uses a 26-pin rectangular disk connector that’s physically incompatible with the 20-pin rectangular connector of other vintage Apple computers. But it turns out that Apple didn’t innovate much in their Disk III design, and the leftmost 20 pins on the Apple III disk connector are the same as the 20 pins of the standard Disk II connector (the remaining 6 pins are used for daisy chaining and auto-sense). All that’s necessary is an appropriate 20-to-26 pin adapter cable, and this guy on Tindie will make it for you! Update: a similar adapter cable is also available on eBay.
Patrick reports that he’s been successful patching in the Floppy Emu as the Apple III’s internal drive, as well as using it as the sole external drive, and also daisy chaining it behind another Disk III external drive. It can be set up as drive 1 and boot the Apple III without any real floppy media, or set up as a higher numbered drive, and used after booting the Apple III from a real floppy in drive 1. According to Patrick, there occasionally will be errors, because the Disk III drives were either slower or faster than Disk II, but for the most part it works with very little issue. (Can anyone confirm this? I thought the drives were the same speed.)
Lots of Apple III software is available at apple3.org.
The only tricky part is getting the correct gender of connector on your adapter. I’ll admit that I’m confused by the Tindie seller’s description of the gender on his adapters, because they seem backwards to me. Maybe he’s referring to the gender of the connector shroud, which is the opposite of the actual pins? To be clear, this is what I mean by a female connector:
And this is a male connector:
The 26-pin connector on the Apple III logic board is male, as are the 26-pin daisy chain connectors on the Disk III drives. The Floppy Emu has a 20-pin male connector on its PCB. With a 26-pin female to 20-pin female adapter cable, you’ll be all set. The Tindie seller has these.
The female-to-female adapter cable isn’t necessarily the most convenient solution, however. Reaching the 26-pin male connector on the Apple III logic board is a major pain, because it involves taking apart the case, and removing the entire internal drive just to get access to the port. A simpler alternative is to disconnect the existing 26-pin cable from the internal Disk III, and then attach that cable to a 26-pin male to 20-pin female adapter cable to reach the Floppy Emu. The Tindie seller has these, but they’re only a couple of inches long.
A third alternative is a very short 26-pin male to 20-pin male adapter, combined with the existing 26-pin cable from the internal Disk III, and with the 20-pin cable that ships with the Floppy Emu. But nobody sells these.
In the end, you might need to make your own cable adapters. It’s not difficult, but if you experiment with homemade adapters, please be careful not to release the magic smoke from your valuable electronics!
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You are correct that the Apple /// drives (both internal, and the Disk /// external) run at exactly the same speed as the Disk II. The motor speed is 300 RPM, and the controller on the Apple /// motherboard uses the same clock frequency, so there should be no difference at all.
The 26-pin header has three signals beyond what a normal Apple Disk II 20-pin cable has. Two of these are the additional select lines for the daisy-chained drives, and each drive’s analog board shifts those select lines one position. The third extra signal indicates whether the Apple /// is in Apple II emulation mode.
The reason for the emulation mode signal is that the Disk /// has an extra circuit to sense disk change, which the Apple /// SOS operating system uses to avoid accidentally writing to the wrong disk if the user happens to swap disks at an inopportune time. This works by detecting transitions from the write protect sensor, and setting a latch that causes the read data from the drive to be suppressed. In Apple II emulation mode the disk change detect circuit is disabled, since Apple II operating systems don’t know about it.
I recently discovered that the strange DB-25 connector uses on the Apple DuoDisk 5.25 dual drive matches the pinout of the Apple ///+ floppy connector (also DB-25). I don’t have either an Apple ///+ or a DuoDisk 5.25, but @jrobj_ on Twitter confirmed that the DuoDisk connected to an Apple ///+ passes the diagnostic test for the disk change detection.
Hi Steve,
unfortunately this adapter is out of stock for over one year.
I am no confident that it will be produced again.
Do you know any other source?
Can you produce that on your own ? Maybe i just need some PIN Schematics to create one.
Best Regards,
Benjamin
Could you sell a converter PCB or cable?
I have an Apple III & Floppy Emu is a must on the computer.
Sell it for 30$ or something.
Would be happy to test such of converter if needed.
Unfortunately I don’t have any Apple III equipment with which to design or test an Apple III cable. From the Tindie photos, it looks like it’s basically a 20-conductor ribbon cable with a 26-pin connector on one end.
Update for others.
So far I’ve confirmed the FloppyEmu works on Apple III with the converter cable (don’t know about Apple III Plus as I don’t have that but my guess is it will).
You can use the FloppyEmu as a primary drive replacement or it is also recognized on drive 2 but you can’t boot from that. So making an Apple IIc like adapter for Apple III is the next major step to make this happen.
Cables are pretty easy to make or looks like someone just started selling them on Ebay: https://www.ebay.com/itm/Apple-III-Disk-III-to-Apple-Disk-Drive-Adapter-Use-the-Dependable-Disk/143389190465
I sure would like to hear from someone who has made this work. I made an adapter based one the photo but can’t get it to work. Coryengelgmail
Ok, quick update. In the first picture that shows the short adapter, the female connector on the left does not have the little tab in the center that ensures it is inserted correctly. I assumed because I didn’t see it that it was in the back where it couldn’t be seen. But no, it just isn’t there. So that means that the tabs on the male and female end, if using a right-angle connector as shown in the photo, should be facing OPPOSITE each other.
Unfortunately, after fixing this, it now does *something* (dim flashing activity light), but my Apple III won’t start while it is connected. Fortunately I don’t seem to have damaged anything but I’m bummed it doesn’t work. I’m using Model C V. 1.7.
@Cory “I sure would like to hear from someone who has made this work.”
— I’ve made this work with a “Drive-Enable” pin swap switch to make the external drive act as internal one (like Steves Apple IIc adapter works). You can only boot FloppyEmu off internal drive FYI.
https://twitter.com/zezba9000/status/1307537524860964865
Thanks to Andrew: the problem is that the little center nubs that ensure plugs with the correct orientation need to be facing each other, contrary to the example pictured above in the blog. Glad that nothing got fried!
No wait—the picture is correct! I guess I’ve finally fried my brain.
I made a little adapter for the “Apple III to Floppy Emu” connection. I didn’t want to swap cables, since my Floppy Emu sits in a nice Disk II-like enclosure. Swapping cables meant I had to disassemble my FloppyEmu enclosure every time. The adapter works with FloppyEmu’s stock cable. It can be connected to the internal or external Apple III port. Unfortunately, the internal connector only supports one drive (= the boot drive). The FloppyEmu’s dual drive support works nicely with the Apple III external connector though – however, the Apple III cannot boot from an external drive.
It’s also possible to use the adapter to connect a normal Disk II drive to the Apple III. But connecting FloppyEmu makes much more sense, of course.
Details here:
github.com/ThorstenBr/AppleIII_diskII
Great job on the Apple III adapter, and nice write-up!
Quick update: I eventually noticed the Apple III indeed has another twist. It has an extra feature to improve disk performance which the Apple IIs do not have – and which results in differing drive control signals when using multiple drives. Do not use simple adapter cables, which simply strip the top 6 wires, in order to connect a FloppyEmu to an Apple III! It will eventually result in corrupted disks – and also cause occasional signal conflicts (multiple drives outputting data at the same time – which is not good). I have improved my FloppyEmu adapter PCB for the Apple III, to properly handle the difference (see updated PCB design in my github).
For those interested in the details of Apple II/III drive control signals: I wrote a longer blog post explaining the details, how the Apple III drive control differs from the Apple II. See over here:
applefritter.com/comment/100359#comment-100359
@ThorstenB @Steve Do either of you plan on selling pre-built or assembly kits for these? I’d love to get one without having to send off for a PCB & parts. Would be cool if Steve was a re-seller or sell solder kits on Ebay.
I have one of the adapters bought on tindie and I can confirm the Floppy Emu works with the A3 no problem. In fact I’m currently toying with it again right now. I’d probably need to build myself one of the switch box to be Elbe to connect externally but configured as internal. For now the emu is connected internally to help things.