Re: cassette interface data format?

[Benjamin Ketcham <bketcham@drizzle.com>]

Michael J. Mahon <mjmahon@aol.com> wrote:
> 
> The best "documentation" of cassette format is in the monitor
> listing for the code that creates and decodes cassettes.  The
> listing is in virtually all early Apple II Reference Manuals.

Yes, I'd like to get my hands on a manual (again).  I had started
to trace the monitor code, but the info you gave below sure saves
me a lot of time and uncertainty.

> There is a lead-in tone of 3.5 seconds of 770Hz, followed by
> a 1-cycle "start" mark with two 400 microsecond half-periods.
> Then data follows, most significant bit first, with two 250
> microsecond half-periods for a "0" and two 500 microsecond
> half-periods for a "1".  Following the data, there is a single
> checksum byte, which is the EOR of all data bytes, seeded
> with $FF.
> 
> Applesoft BASIC files are preceded by a short record with
> the length of the program and an "auto run" flag byte.

Thank you very much for this info!  If it is available on the
Web anywhere, I was unable to find it with my search attempts.
I'd suggest that those who maintain Apple II FAQs (there seem
to be more than one active FAQ) might want to include this
info -- though I guess if I'm the only one who asked, it's
not a very FA Q.

--Benjamin