Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!mailrus!iuvax!bsu-cs!cfchiesa
From: cfchiesa@bsu-cs.UUCP (Christopher Chiesa)
Newsgroups: comp.sys.atari.8bit
Subject: Re: Need a cassette tape drive.
Summary: Cassette drive NOT a typical peripheral!
Message-ID: <4417@bsu-cs.UUCP>
Date: 20 Oct 88 19:54:47 GMT
References: <736@wsccs.UUCP> <4408@bsu-cs.UUCP> <2170@udccvax1.acs.udel.EDU>
Organization: CS Dept, Ball St U, Muncie, Indiana
Lines: 85


In article <2170@udccvax1.acs.udel.EDU>, gdtltr@vax1.acs.udel.EDU (Gary D Duzan) writes:
> In article <4408@bsu-cs.UUCP> cfchiesa@bsu-cs.UUCP (Christopher Chiesa) writes:
   [disk preferences over cassette, deleted...]

> >3) I don't imagine the interface to a standard tape recorder should be too
> >   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
> >   direct connection here) to turn the cassette player's MOTOR on and off in
> >   response to the appropriate SIO signals.  (On the other hand, you could
> >   probably get away with leaving it ALWAYS on, in some if not all cases.  There
> >   ARE cases where the computer NEEDS to start and stop the tape, however.)
> >
>    I think you will find it more complicated than you think. Remember that all
> I/O devices attached to the SIO port MUST BE INTELLIGENT!!! I believe the
> 1050 drive has a microprocessor almost as powerful as the 6502 (not a great
> statement, but it is better than nothing). 

Alas, I have a bone to pick with you on this information, Gary.  Are you sure
you're not confusing the CASSETTE drive (and interface) with a DISK drive and
interface?  I don't quite see the connection between the original question of
creating a cassette interface, and the microprocessor in the 1050 disk drive.
The original posting had nothing to do with the 1050 or any other DISK drive;
the poor fellow simply stated that he wanted to build an interface for CASSETTE.

Normally, you would be quite correct in stating that such a project would be
complex because the resulting SIO device "MUST BE INTELLIGENT" -- but in the
case of the cassette drive and interface, that is NOT so.   To wit:

   OS Listing, page 42 (line 1736, within the SIO Controller code): 

    "All devices EXCEPT CASSETTE are inteligent."  

   OS User's Manual, section 3, under "Program Recorder":

    "The ATARTI 410 [TM] Program Recorder is a special peripheral.  It uses
     the serial bus to send and receive data, but does not conform to the 
     protocol of the other peripherals that use the serial bus."

That pretty well defeats the argument that the interface is complex in terms
of its requiring INTELLIGENCE; however, you may still have a point, which I
implicitly conceded in my first posting, that the data MAY or MAY NOT be 
transmitted back and forth as audio tones.  

> An SIO call sends data to the
> processor on the device and the device responds with the proper data, not just
> some sounds. 

I'm sure this is true, in most cases, but the CASSETTE as noted is treated
differently.  Section 11 of the OS User's Manual, under "SOUND GENERATION," 
refers obliquely to "... cassette FSK tone generation," and chapter II,
section C, page II.26 (my God, I sound like a lawyer; forgive me!) of the
Hardware Manual states that "Output data is normally transmitted as logic 
levels (+4V=true 0V=false).  Data can also be transmitted as two tone
information.  ... In this mode audio channel 1 is transmitted in place of 
logic true, and audio channel 2 in place of logic zero." 

Taken together, it sure SOUNDS (no pun intended) as though the cassette WRITE 
operation, at least, is performed in two-tone mode.  Unfortunately, there is 
no corresponding informaition implying or stating ANYTHING about cassette
READ operations. 

> There is a pin on the SIO to allow an audio signal to pass though
> the computer and out through your monitor speaker and a motor on/off pin, so
> you could probably get it to play, but reading data off it is out of the
> question without a processor chip.

Au contraire; it seems rather likely that he could get it to RECORD data, and
that PLAYING BACK data is at worst still "up in the air."  I'd say he still
has a shot at it. 

And if he succeeds and tells us how he did it, ya know what I'm gonna do?  I'm
gonna develop some really cool software here at home, at leisure, then save
it to cassette as a casette-bootable binary, make a special adapter for my 
Walkman to connect to the Atari SIO port, take the whole shootin' match to
the local department store's Atari XEGS display area, and quickly upload a 
sharp-looking showoff demo!  They won't know where the heck it came from,
unless I specifically tell 'em.  Hehehe.

   Chris Chiesa
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