parallel port SCSI controller

[Jules]

Has anyone come across a schematic for a PC parallel port SCSI controller?
I think I've got one figured out on paper but I'm surprised nobody's
produced a hobby version already and it seems a shame to reinvent the
wheel.

For my particular application I'm only talking to old SCSI-1 devices so
lack of speed is not a problem - hence I'm hoping I'll be able to get
away with a dumb interface just using a few buffers and latches, rather
than a microprocessor controlled solution with buffering which handles the
SCSI protocol. I don't yet know if I'm going to hit timeout problems
though...

cheers

Jules

 

[Si Ballenger]

On Sun, 30 May 2004 16:34:05 +0100, Jules
<julesrichardsonuk@remove.this.yahoo.co.uk> wrote:

Has anyone come across a schematic for a PC parallel port SCSI controller?
I think I've got one figured out on paper but I'm surprised nobody's
produced a hobby version already and it seems a shame to reinvent the
wheel.

For my particular application I'm only talking to old SCSI-1 devices so
lack of speed is not a problem - hence I'm hoping I'll be able to get
away with a dumb interface just using a few buffers and latches, rather
than a microprocessor controlled solution with buffering which handles the
SCSI protocol. I don't yet know if I'm going to hit timeout problems
though...

cheers

Jules

Some of the older parallel port scanners have cables that
apparently do the parallel port/scsi interface work. You might
find some info in those types of areas.

 

[Klavs Rommedahl]

Jules <julesrichardsonuk@remove.this.yahoo.co.uk> wrote in message news:<pan.2004.05.30.15.34.05.264841@remove.this.yahoo.co.uk>...

Has anyone come across a schematic for a PC parallel port SCSI controller?
I think I've got one figured out on paper but I'm surprised nobody's
produced a hobby version already and it seems a shame to reinvent the
wheel.

For my particular application I'm only talking to old SCSI-1 devices so
lack of speed is not a problem - hence I'm hoping I'll be able to get
away with a dumb interface just using a few buffers and latches, rather
than a microprocessor controlled solution with buffering which handles the
SCSI protocol. I don't yet know if I'm going to hit timeout problems
though...

cheers

Jules

I have one "builded" in a box. Maybe i can open it and reverse
engineer if You want ?
Rgds
Klavs.

 

[Jules]

On Thu, 03 Jun 2004 12:33:59 -0700, Klavs Rommedahl wrote:

I have one "builded" in a box. Maybe i can open it and reverse
engineer if You want ?

hiya,

That would be quite useful. I'm curious to see how other designs have
managed to get around the lack of output lines on a PC's parallel port.

I figure I need octal tri-state latches for data out / in (I'm assuming a
bi-directional port) and for the outgoing SCSI control lines.

There are enough input lines for me put all of the 'incoming' SCSI
control lines via a buffer straight into the port.

Still means I need three seperate latches though, which means two of the
parallel port outputs are needed to control a 2-to-4 line decoder to
select which latch to address.

Problem is that any one latch needs to be held in a latched state whilst
I select a different latch using the decoder - so there are two possible
sequences for the latches:

1) select latch using decoder
2) latch a low into the selected latch's control pin (assuming control is
active low for the moment) in order to latch data.
3) latch a low into the selected latch's output enable pin (again assuming
active low).

or:

1) select latch using decoder
2) latch a high into the selected latch's output enable pin to set the
outputs to high impedance.
3) latch a high into the selected latch's control pin in order to stop
latching data and make internal register follow inputs.

in other words ideally I need three controlling lines here and only have
two spare available (as the PC parallel port only has four output control
lines and I need two for the decoder). When "setting" the latch I need to
latch data first, then set outputs to low impedance, but when "clearing"
the latch I need to do the opposite and set the outputs to high impedance
*before* clearing the latch.

I'm curious as to how this has been done in the past given the small
number of output lines available on the PC's port. Unless of course all
the designs work in slower nibble mode rather than dealing with 8 bits at
a time...

cheers

Jules

 

[the Wiz]

Iomega had them for some of their external cartridge drives. I may still have
one...

Jules <julesrichardsonuk@remove.this.yahoo.co.uk> wrote:

Has anyone come across a schematic for a PC parallel port SCSI controller?
I think I've got one figured out on paper but I'm surprised nobody's
produced a hobby version already and it seems a shame to reinvent the
wheel.

For my particular application I'm only talking to old SCSI-1 devices so
lack of speed is not a problem - hence I'm hoping I'll be able to get
away with a dumb interface just using a few buffers and latches, rather
than a microprocessor controlled solution with buffering which handles the
SCSI protocol. I don't yet know if I'm going to hit timeout problems
though...

cheers

Jules

More about me: http://www.jecarter.com/
VB3/VB6/C/PowerBasic source code: http://www.jecarter.com/programs.html
Freeware for the Palm with NS Basic source code: http://nsb.jecarter.com
Drivers for Pablo graphics tablet and JamCam cameras: http://home.earthlink.net/~mwbt/
Email here: http://www.jecarter.com/contactme.htm

 

[Watson A.Name - \"Watt Su]

"Jules" <julesrichardsonuk@remove.this.yahoo.co.uk> wrote in message
newsan.2004.05.30.15.34.05.264841@remove.this.yahoo.co.uk...

Has anyone come across a schematic for a PC parallel port SCSI
controller?
I think I've got one figured out on paper but I'm surprised nobody's
produced a hobby version already and it seems a shame to reinvent the
wheel.

For my particular application I'm only talking to old SCSI-1 devices
so
lack of speed is not a problem - hence I'm hoping I'll be able to get
away with a dumb interface just using a few buffers and latches,
rather
than a microprocessor controlled solution with buffering which handles
the
SCSI protocol. I don't yet know if I'm going to hit timeout problems
though...

cheers
Jules

Makers such as Adtron have adapters that go from IDE to SCSI, or USB to
SCSI. It's not worth it to mess with parallel ports when you can get a
plug and play solution for a few tens of dollars.