[Coco] History of Tandy/Radio Shack Cassette Recorders

[Aaron Banerjee]

(this is regarding "inverted" cassette signals)
John,
> 
> In all of the time that I have looked at home computers and cassette 
> data storage, this is the first that I have heard of this issue of 
> inverting the signal, and it does not seem to make sense.
> 
> Since it is a frequency, not level modulated signal that is AC coupled, 
> I find it hard to believe that anything would care if the signal was 
> inverted.

    Not if you're using a zero-crossing detector to measure your
frequency..  Instead of going into a lengthy explanation, it's well
documented (if you're interested) in US Patent #4,468,752 -- all the way
down to the CLOAD sourcecode.  The easiest way to get a copy of the patent
is to goto www.uspto.gov and do an "Patent Number Search" through issued
patents.  It is entitled "Data Synchronization Apparatus"
    One of the things I found interesting is that the coco uses 1 cycle of
2400 hz for a "1" and 1 cycle of 1200 hz for a "0" -- which is exactly
what caller ID did (at least at one time).  I had thought about figuring
out some way to hook up a coco to the phone line and have a "smart"
caller-id box (e.g. if number = telemarketer then hang up using the
cassette relay).

          - Aaron