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From: dml@loral.UUCP
Newsgroups: comp.sys.m6809
Subject: Re: CoCo3, Disto Controller, OS-9
Message-ID: <1389@loral.UUCP>
Date: Wed, 11-Mar-87 13:46:33 EST
Article-I.D.: loral.1389
Posted: Wed Mar 11 13:46:33 1987
Date-Received: Fri, 13-Mar-87 20:47:28 EST
References: <1608@lsuc.UUCP> <15129@amdcad.UUCP>
Reply-To: dml@loral.UUCP (Dave Lewis)
Distribution: na
Organization: Loral Instrumentation, San Diego
Lines: 38
Summary: Single density, how-to

In article <15129@amdcad.UUCP> bandy@amdcad.UUCP (Andy Beals) writes:
>In article <1608@lsuc.UUCP> jimomura@lsuc.UUCP (Jim Omura) writes:
>>problem is that the WD-1773 chip doesn't seem to read/write single density.
>
>The 1773 definitely does read/write single density.  Your vendor probably
>doesn't program it correctly. :-(
>	andy

  The single/double density select on Radio Shack and J & M disk controllers
is address $FF40, bit 5 ($20): 0 = single density, 1 = double density. Other
manufacturers (Disto, etc.) probably do the same thing, but I can't be sure
as I don't have a Disto controller.

  The Radio Shack BASIC disk routines, and the RS/Microware CCDisk in OS-9,
are both hard-coded with this bit set to a 1 for double density. I have
considered writing single-density support into the new disk driver that I'm
working on, but it would be a lot of trouble (and code, on a memory-limited
machine) for little return. In fact, when I asked for responses to "what
features would YOU like to see", the few answers I got rated it of very low
importance.

  If some determined hacker out there wants to add single-density support to
my NewDisk driver, you have my blessing. I'll even send you a copy of the
source (freely distributable, just give me credit for the parts you use).

-------------------------------
          Dave Lewis    Loral Instrumentation   San Diego

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