[Coco] Strange.... two 40 track disks on one 80 track disk?

[Arthur Flexser]

Of course, if his drives are single-sided, no amount of poking will let him
access the back!

Art
On Sat, Oct 31, 2009 at 8:25 PM, Christopher Hawks <chawks at dls.net> wrote:

> Fedor Steeman said the following on 10/31/2009 03:50 PM:
>
> Hi,
>>
>> Some time ago I acquired this huge collection of diskettes that were part
>> of
>> a user group's CoCo software library. A lot of these are backups of
>> backups
>> so there is bound to be a lot of stuff I will be able to recover.
>>
>> There are a large number of diskettes that seem to contain a backup of two
>> 40 tracks diskettes on one side of an assumed 80 track diskette.
>>
>> However, I can only access the first diskette of each of these backup
>> floppies. I know because some of them have their contents listed on the
>> envelope (or whatever you called the paper bag the diskette is in).
>>
>> I have a drive that can be switched from 80 to 40 tracks but that made no
>> difference.
>>
>> Is there some way in HDB DOS that I am using (or RSDOS for that matter)
>> that
>> would enable access to the other 40 tracks and thus the other diskette
>> backup?
>>
>
> Fedor:
>
>        It may be that the other tracks are on the other side of the disk
> (not as in a flippy).
>
>        On a Coco 3 (or a 1 or 2 in ram) with DECB 2.1 (1.1), POKE &HD89F,
> &H40 will make drive 2 the backside of drive 0. Likewise POKE &HD8A0,&H41
> will make drive 3 the back of drive 1. There a 4 memory locations that are
> the drive mask (&HD89D - &HD8A0) the relevant bits are:
> bit 0 - drive select 0 (&H01)
> bit 1 - drive select 1 (&H02)
> bit 2 - drive select 2 (&H04)
> bit 7 - side select    (&H40)
>
>        These can be manipulated to access any side of any (physical) drive
> as any drive number.
>
> --
> Christopher R. Hawks
> HAWKSoft
> ---------------------------------------------------------
> Never meddle in the affairs of NT. It is slow to boot and quick to crash.
>        -- Stephen Harris
>
>
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