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Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!netsys!c3pe!c3sw!charles
From: charles@c3sw.uucp (Charles Green)
Newsgroups: comp.sys.atari.8bit,misc.wanted
Subject: Re: Need a cassette tape drive.
Summary: 5 Megabytes on a cassette
Keywords: XR2211 FSK
Message-ID: <4216@c3pe.UUCP>
Date: 2 Nov 88 01:56:01 GMT
References: <736@wsccs.UUCP> <4408@bsu-cs.UUCP>
Sender: news@c3pe.UUCP
Reply-To: charles@c3sw.UUCP (Charles Green)
Organization: C3 Incorporated, Software Engineering, Herndon VA
Lines: 40

In article <4408@bsu-cs.UUCP> cfchiesa@bsu-cs.UUCP (Christopher Chiesa) writes:

>1) You don't need an 'interface' if you obtain an Atari cassette drive - they
>   are made to plug right into the SIO port, although they have only ONE SIO
>   connector and therefore "terminate" any daisy chain.  (This implies that

The Atari 1010 program recorder (I have one) has two SIO connectors.

> I HAVE heard, however, from a friend who got the new XM551 drive and does NOT
>   like it...

I have the Atari 1050 disk drive, and DO like it, although I wish it did "true"
double density, with twice the data storage of single-density, rather than
half again.  And imagine what 512-byte sector support could do for program
interchange: "Sure, I can read that PC-DOS diskette!" (Happy Computers Inc,
are you listening?).

>   about Mike W's experience; 'aegnor' is the one who was telling ME.)
>   complicated; data is stored and retreived as audio tones on, I believe, 
>   the LEFT channel of a standard stereo recording, with capability to play
>   right-channel audio through the TV/monitor speaker!  You should be able  
>   to simply connect the audio inputs, outputs, and ground, to the appropriate
>   SIO pins, as well as using some kind of control circuit (I do NOT recommend

As already pointed out, the Atari uses the Pokey two-tone mode to output FSK
on the serial output pin.  (This FSK is, alas, apparently not phase-coherent,
which may be why we are limited to 600 bauds.)  Thus, you can *record* Atari
tapes, with no further electronics, on a standard cassette deck.

To read them back, however, you must present the decoded data to the serial
input pin.  That requires an FSK demodulator, the only "magic" in the Atari
program recorder.  Before I bought my Atari 1010, I bought an Exar XR2211 FSK
Demodulator chip, and got excellent results writing and reading tapes.  In
fact, the 1010 gave much *worse* performance than my simple one-chip solution!

One of these days, I'll do some serious experimenting with some custom tape
I/O software and the XR2206 (phase-coherent) FSK modulator. If a Bell 103
can do 300 baud in 1.5kHz bandwidth, 12kHz on a tape deck would give 4800bps
and using all four tracks in a stereo deck will yield 5 Megabytes on a C-90.
-- 
Charles Green	charles@c3pe.UUCP	{decuac,cucstud}!c3pe!charles