All members are invited to blog on Applefritter. Weblogs should generally be of a technical nature and should be written in such a way as to still be readable and useful 50 years from now. Please do not embed outside media. Images and videos can be uploaded via the Media Browser. Files should either be attached to the blog post or uploaded to the file libraries.

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Using the "Phi1 Echo" to distinguish disk controllers

Apple hid a quirky feature inside its disk drives, a full-loop signal path via addressable latch Q1, via stepper phase-1, via the motor control board, via the write-protect switch, via the analog board in the disk drive, via the shift-right input into the data register, and back onto the bus.  This signal path can be used to distinguish between the various Apple II disk controllers.
  • Apple Disk II controller prints 2 inverse bytes: 7F 00
  • Micro Sci A2 controller prints 2 inverse bytes: 80 00
  • (untested guess) IWM in Apple //c: A0 20
  • (untested guess) IWM in Apple //c+: AF 2F [EDIT: this guess was wrong]


Infocom Font RC 1003.pdf

The first working(-ish) homemade MMU

Back in early march, I dug out my old Apple IIe computer from my parents's garage. That was a fantastic find and I wanted to play again all those games from my childhood. Unfortunately, the computer did not power on. While searching on the internet, I was sidetracked while reading on the MMU and IOU and their lack of replacements. And then I foolishly though that attempting to re-create the MMU and the IOU with a FPGA would be a good idea. Surely, it can't be that hard...


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