Re: [PARPORT] SCSI-1 emulation?
Thu, 11 Feb 1999 06:59:33 -0500 (EST)

> Just a thought (as I sit here trying to figure out how to make this dang
> zip drive work w/o a scsi card... ;) ) ...
> There are 25 pins on a scsi-1 connector... there are 25 pins on the
> parallel port... I know that "spp" has no means of reading input (except
> those 5 response pins), but what about other modes?
> Is it possible to emulate a scsi controller on the parallel port?

There are many products out there that do essentially what you suggest.
Iomega even makes ZIP drives with such an adapter built it ;-)

Apparently, there is even an assembly language programming textbook
out there somewhere that has a recipe for a DIY PP SCSI adapter.

I'd be interested in seeing that reference if anybody can recall it.

But, you would find that such a SCSI adapter was intolerably slow, as
the REQ/ACK handshaking would have to be done entirely in software. This
is acceptable for things like command delivery or fetching status, but
not for data block transfers.

The "real" PP SCSI adapters contain buffering, some kind of phase-locked
ACK generator, and possibly a more elaborate SCSI state machine. Some
even contain a bargain basement ISA SCSI adapter (like a 5380). And, of
course, they have to have some sort of nybble-mode multiplexor to be able
to handle SPP ports.

I don't know about where you live, but here you won't find an enormous price
advantage of a PP SCSI adapter over a low end ISA SCSI card. The main
reason people use PP adapters is so that they don't have to have two
different SCSI adapters for their desk and laptop machines.

As for Linux support, currently the Iomega "Jaz Traveller" is probably the
only external adapter that is really supported. I have some old alpha
drivers for some of the other common adapters. BUT, work is underway to
bring out a "grand unified" ppSCSI driver within the next few months.

Grant R. Guenther

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This archive was generated by hypermail 2.0b3 on Thu 11 Feb 1999 - 07:07:03 EST