Re: HD20

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

Michael J. Mahon <mjmahon@aol.com> wrote:

> David Empson suggested:
> 
> >> you <you@somehost.somedomain> wrote:
> >> 
> >> > and it is twined by another 28 pin that is marked: 625v  
> >> > c244....VP4060-0001....344-0041-B...c Apple 1982 1983
> >> 
> >> Probably an IWM.  I don't have anything handy which contains one (short
> >> of dismantling a IIc) so I can't easily check the number.
> >
> >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).
> 
> Could someone enlighten me about the function of an IWM in a
> Smartport to SCSI converter?  I thought the IWM was basically
> a Disk ][ controller on a chip.

It is also used to implement the SmartPort communication over the bus.
In a UniDisk 3.5, the IWM serves a dual function: it can communicate
with the host computer, and can control the drive mechanism (an I/O
location under CPU control switches the IWM's I/O signals between the
two).

> It must be more than that.  Does it implement Smartport protocols
> (which I thought would be in firmware).

The IWM's support for the SmartPort protocol is limited to its ability
to send 7-bit data over the bus, plus dealing with a few sense lines -
it provides the physical interface.  Software is responsible for the
packet structure, 7-and-1 data splitting, command set, etc.

-- 
David Empson
dempson@actrix.gen.nz