Nine-Track (9-track) 800bpi NRZI Format decoding

I really appreciate the confirmation of 0x13, because the ANSI documentation you shared is "clear as mud" on this topic for me. I don't know how this description translates to 0x13, BUT, I AM seeing 0x13 twice at the end of my tapes, so your real-world description overrides my confusion from this ANSI document.

I had no idea how `1 bits in tracks 2, 3 and 8` translates into binary `00010011`. tracks 2, 3, and 6, maybe if you start counting backwards where Parity is track 1, but not 2, 3 and 8....No matter how I arranged it, I got a totally different value from this.

You know, in typing that last message out, I think I just figured out why that ANSI document was SO confusing to me...they renumbered all of the tracks with their own 1-9 numbering system, starting from one of the tape edges, and never really gave a diagram like this saying how their numbering system "maps" to the real-life track names. I guess for ANSI documents, they need to add this additional layer of obfuscation to make their attorneys happy? Anyway, I think I'm getting it through my thick head now.  If I take their diagram and re-draw it like this:

Yeah, I see it now...from left to right

00010011  - 0x13 "TapeMark"
01234567P - real world tracks
765391824 - ANSI track order

OK, 3, 8 & 2, or 2,3 & 8... got it now! Anyway, the main point of my message was to say "Thank YOU" on this, and I know I went a bit overboard.

I really should put these last 2 messages into one of my blog posts. It could help the next less-technical person like myself who dares enter this territory...

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SimH .tap files:

larsbrinkhoff — March 14, 2024 at 2:50 AM

Your entire .tap should look like this:

17 of these: "FC 0F 00 00" <4092 bytes> "FC 0F 00 00"

(FC 0F 00 00 is little endian for 0xFFc which is 4092 in decimal)

1065 of these: "3C 0F 00 00" <3900 bytes> "3C 0F 00 00"

End of tape: "00 00 00 00  00 00 00 00"

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Link to my Lotus Notes database program decoding this: