S.Elliott's blog

WIP: Tape Port Test patterns

Synopsis: an information-capture for work-in-progress

The Apple cassette save routines use the Y register to determine the pulse-width between signal edges, and there are seven distinct values for the Y parameter depending upon the context and state of the save routine.  For the purposes of studying the cassette routines, I named each parameter for its default value and tested their limits:


Ultima V MIDI with hidden arrangements

For preservation:

A collection of MIDI files extracted from Ultima V in 1995, copied through a MIDI cable to a Roland SCC-1, saved for decades on a 3½" floppy disk, reproduced here on a GS-compatible Roland MT-120.

A full performance is recorded here, and on YouTube.

Artifacts hidden inside the MIDI data reveal hidden arrangements and sound effects that were not reproduced during game play -- including percussion and sound fx that were probably reproducible only on the original composer's equipment.

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]


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