Bart <who@where.what> wrote:

> >The square pack IWM in the IIgs has a part number of 344-0041-A and a
> >copyright date of 1982, so it seems very likely that this is an IWM.  It
> >might be a specially modified version (indicated by the 'B' suffix).
> >
> >
> So....if a modified IWM is in use here, and if this is indeed a
> SCSI<>Floppy solution as it seems to be....  The Rodime indeed looks like
> a SCSI and nothing at all like a SIDER SASI or a ProFILE type (I have
> both), I think the reason it has this 26 pin connector instead if the
> standard 50 is simple economy. probably learned from the Apple II and the
> HS SCSI card and Rev C:  iirc 25 or one half of the SCSI pins in a normal
> 50 are ground.  would not 1 server for all, hence 26?  (it also comes out
> even that way; odd numbered pins on a ribbon wire would be a bear to
> manufacture!
> ....then....   Is this not almost EXACTLY the Chinook solution?

It certainly looks like it is similar to a SmartPort/SCSI adaptor, but
I'd expect the same sort of arrangement for any intelligent peripheral
which connects to the disk port of an Apple II or Mac.  The UniDisk 3.5
has a similar combination of components (without the big ASIC).

I'm dubious about the drive having a SCSI interface, as there is no sign
of a SCSI controller chip (NCR 5380 or 53C80) on the main board.

The 68-pin square pack ASIC could conceivably be implementing a limited
subset of SCSI, only supporting one device.  On the other hand, The
26-pin interface may be something proprietary which Apple and Rodime
cooked up.

> And, if so (now rememeber gang I know squat about this so I am talkin through
> my hat), then would not a different firmware, or other such work for modifying
> a HD20 to be accessable from a //c?

Potentially, yes.  I expect that the interface is using a SmartPort-like
protocol, but it obviously isn't standard SmartPort, because the drive
doesn't work on a IIc.

The biggest hurdle is that the Mac and Apple II use pin 10 of the disk
connector for different purposes.

On the Mac, pin 10 is a motor speed control output, used by the original
400K and 800K 3.5" drives.  It is one of the control lines from the VIA
chip, which can generate a square wave output, handshake signal, or be
controlled directly by the CPU.  The VIA can be configured to make this
pin an input, but I expect that there is buffering hardware on the Mac
motherboard which requires that it is an output.  (In addition, any 3.5"
drive in the daisy chain will buffer and output the signal to the next
drive, so there is no possibility that this signal could be set as an
input on the Mac.)

On the Apple II, pin 10 is the write protect sense input from 5.25"
drives.  It is also used by the SmartPort protocol as an ACK signal from
the drive to the host.

Because this pin is an output on the Mac, it is likely that the
controller board in the HD20 is only able to use this signal as an
input, and it could be involved in the communication protocol between
the Mac and HD20.

If so, it would not be possible to support the HD20 protocol in software
on an Apple II, and it would also not be possible to modify the HD20
firmware to use the SmartPort protocol, unless some hardware hacks were
made in the drive so that it can output a signal on this pin.

-- 
David Empson
dempson@actrix.gen.nz