Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!bbn.com!slackey
From: slackey@bbn.com (Stan Lackey)
Newsgroups: comp.sys.atari.8bit
Subject: Re: Need information on double-density SIO commands
Keywords: R W P DCOMND DBUFLO/HI
Message-ID: <40946@bbn.COM>
Date: 5 Jun 89 18:49:29 GMT
References: <7097@c3pe.UUCP>
Sender: news@bbn.COM
Reply-To: slackey@BBN.COM (Stan Lackey)
Organization: Bolt Beranek and Newman Inc., Cambridge MA
Lines: 28

In article <7097@c3pe.UUCP> charles@c3pe.UUCP (Charles Green) writes:
>Now that I have an Atari drive that can read and write 256-byte sectors, I'd
>like to try accessing floppies from a CP/M machine in our office, which can
>write 40-track, single-sided, double density 256-byte sectors.  However, I
>haven't been able to successfully use SIO to read the sectors.
>
>I have a BASIC program with machine language assist which can read/write the
>standard 128-byte sectors via SIO calls, stuffing 'R' into DCOMND and filling
>in the other fields of the DCB for sector number and buffer.  I hoped that by
>putting 256 into DBYTLO/HI I would be able to read the sectors, but I only got
>data for the first three sectors, which leads me to believe I'm still only
>giving the "single-density" read command...

It sounds like you have the XF551.  I have hacked around doing exactly what
you are doing.  I believe that the way the density is selected is by using
'R' with the number of bytes; 128 selects single density (which is what the
first three sectors are written in) and 256 selects double density.  That's
all.  Note: the standard SIO entry (the address escapes me) resets the byte
count to 128!  If you have the OS listing, you should be able to figure out
the proper address; that is, the routine that is called after SIO sets byte
count to 128.  I can look it up if you need it.

My mission was to transfer files from IBM PC to Atari.  A kind soul on the
net came to my aid with a program to r/w Mydos 256-sector files with a
PC, and as it turns out Spartados can r/w Mydos disks.  I was prepared
to write all that stuff myself!  It all works beautiful now.

-Stan