Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site ucbvax.ARPA
Path: utzoo!watmath!clyde!burl!ulysses!ucbvax!ardc.arpa!ekijak
From: ekijak@ARDC.ARPA (Edmund S. Kijak, POINT)
Newsgroups: net.micro.atari
Subject: Re:  600xl disk simulation?
Message-ID: <8509241721.AA07193@UCB-VAX.ARPA>
Date: Tue, 24-Sep-85 13:13:35 EDT
Article-I.D.: UCB-VAX.8509241721.AA07193
Posted: Tue Sep 24 13:13:35 1985
Date-Received: Thu, 26-Sep-85 07:38:50 EDT
Sender: usenet@ucbvax.ARPA
Organization: The ARPA Internet
Lines: 11

Regarding the casette interface, I don't see how it can be done entirely in
software.  The casette output is an analog voltage whose magnitude depends
on the volume control setting - you would need some hardware simply to convert
it to a standard voltage level, say TTL.
	The interface converts FSK (frequency shift keyed) audio tones to 
digital bits.  The bits are asynchronous serial with a start bit, data bits,
and a stop bit.  Baud rate is 600, a ZERO is a 3995 Hz tone, a ONE is a
5327 Hz tone, the tone durations are equal.  The output of the casette needs
to be converted to TTL levels (0 or 5 volts for logic ONE or logic ZERO)
before feeding to computer. (I may have the ONEs and ZEROes swapped, and
may be off a few Hz, but the info is basically correct).