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Bootstrapping Apple //c with Floppy Emu

Thanks to Floppy Emu fan Andru Luvisi for contributing a great trick for bootstrapping an Apple //c with Floppy Emu. The Apple II family computers can normally only boot from Disk 1, but when Floppy Emu is connected externally to a //c and configured in 5.25 inch emulation mode, it becomes a non-bootable Disk 2. Until now, the options for making Floppy Emu bootable on a //c were:

  • Switch the Emu’s emulation mode to Smartport hard disk, which is bootable
  • Boot from a real 5.25 floppy in Drive 1, and then access the Emu as Drive 2
  • Connect the Emu internally, in place of the real 5.25 inch floppy drive
  • Use an A/B switch cable to connect the Emu and the real 5.25 inch floppy drive internally

Andru has devised a method for booting the //c from the Floppy Emu while it’s connected externally and configured in 5.25 inch emulation mode. In other words, it’s a method for booting from Disk 2 – something that’s normally impossible. This is great for the scenario where you want to make a bootable ProDOS floppy, and you’ve got a Floppy Emu, but no real floppies with a bootable DOS. Now it’s possible to boot from the Emu externally, then put a blank floppy in the //c’s internal drive and copy ProDOS to it.

  1. Connect Floppy Emu to the //c’s external disk port, and turn on the computer.
  2. The //c will display a CHECK DISK DRIVE error.
  3. Select ProDOS v1.9 from the Floppy Emu’s disk selection menu.
  4. Press CTRL+RESET on the //c keyboard to get a BASIC prompt
  5. At the ] prompt, type CALL -151 and press RETURN
  6. At the * prompt, press CTRL+E, then press RETURN
  7. You’ll see a line of text like M=00 A=08 X=00 Y=00 P=00 S=B7.
    If the line of text begins with M, then type
    :0 E0 60 1 and press RETURN
    Else if the line of text begins with A, then type
    :E0 60 1 and press RETURN
  8. Type C60BG and press RETURN

The //c will immediately begin booting ProDOS from Drive 2!

Andru developed this method by examining code from Apple //c ROM version 255, which includes this feature natively as PR#7. The above monitor hacking makes it possible to do the same thing on other ROM versions of the Apple //c.

I was successful using this method with ProDOS v1.9, as well as with a few other utilities and games. Unfortunately most games won’t work using this method. They’re hard-coded to expect booting from Drive 1, so if you try this method they’ll start to boot from Drive 2, but then you’ll hear Drive 1 suddenly begin to grind away, and the game will freeze or display an error. Despite this limitation, booting 5.25 inch disk images from Floppy Emu as Drive 2 is still a very handy trick!

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1 Comment so far

  1. MG April 22nd, 2017 2:25 pm

    If you are feeling adventurous and have an EPROM programmer, you can install my modified Apple //c firmware which includes a menu that allows you to boot the external drive.

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