8-bit acorn emulators • Re: HFE and Index Pulses

Hopefully a quick question for someone who knows. With the HFE image file format, where should the index pulse be relative to the start of each set of track data from the file? If at the start, is the track data in the file aligned to the leading or trailing edge of the index pulse and how long should it be?

I don't know the correct answer.

I based beebjit's code on various tests and observations:
- HFE tooling (e.g. HxC Floppy Emulator) seems to generate HFEs with the SET INDEX right at the beginning of each track.
- HFE v3 only encodes the start of an index pulse.
- Testing a real disc drive (my Chinon), it sustains the index pulse for about 4ms. This matches datasheets for other drives, which specify 4ms pulse width.
- Testing with a real 1770, the trigger point appears to be the leading edge of the index pulse. Specifically, the "read track" command will start returning track data at the leading edge of the index pulse.


Cheers
Chris

Statistics: Posted by scarybeasts — Fri Apr 25, 2025 7:39 pm

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