Re: Apple IIgs... (UniDisk 3.5)

[dempson@actrix.gen.nz (David Empson)]

<sirarlias@webtv.net> wrote:

> I also have a UniDisk 3.5 on my IIgs (3.5 Drive+UniDisk 3.5+5.25+5.25).
> For some reason, a few programs don't like the idea of the UniDisk 3.5
> being there. One example is Test Drive II: accessory disks such as The
> Supercars refuse to load from it. I have to switch the main Test Drive
> II disk to the UniDisk and install from the standard 3.5. Of course this
> makes an already slow-loading game a lot slower.

Possible explanations:

1. The software bypasses the firmware and expects to access the 3.5"
drive hardware directly, e.g. for copy protection.  This requires
completely different techniques for an Apple 3.5 Drive and a UniDisk
3.5.

2. Badly written software which can only access unit 1 or 2 in slot 5.
In your case (due to having /RAM5 enabled), your UniDisk 3.5 is mapped
as the third unit.  (If the application runs under ProDOS 1.0.x or 1.1.x
then it won't even be able to access the UniDisk - the ability to
support four units in slot 5 was added in ProDOS-8 1.2.)

> Another strange thing that happens is when the UniDisk spins, the drive
> light on the adjacent 5.25 drive dimly flickers.

This is a side effect of the way the control signals work for the
different drive types.  For example, the Apple 3.5 Drive has a special
enable signal, which causes it to disconnect the drive select signals on
the daisy-chain connector.  It cannot do this fast enough to avoid
triggering a brief flash on the select light for a 5.25" drive.

I don't recall the precise details of the UniDisk 3.5 control sequences,
but I expect a similar effect is occurring.

> Oh, while we're on the subject, why is the UniDisk 3.5 recognized as a
> slot 2, drive 1 device instead of 5,2 on the IIgs?

ProDOS-8 1.2 and later remap the third and fourth unit on slot 5 to slot
2 (provided you don't have a disk controller card in slot 2).

The default order for drives is as follows:

- First 3.5" drive
- /RAM5 (if enabled)
- /ROM5 (if available - it is supplied by some memory expansion cards)
- Second 3.5" drive
- Third 3.5" drive
- Fourth 3.5" drive

If you have the startup device set to the RAM disk or ROM disk, then it
will swap places with the first 3.5" drive.

The first two drives are S5,D1 and S5,D2.
The next two are S2,D1 and S2,D2.

If you have more than four devices available via the SmartPort firmware,
you cannot access the rest via ProDOS unless you are running ProDOS-8
2.0.1 or later, which can remap additional drives to other unused slots.