[rescue] Parallel ports [was Re: Slightly OT: ?Bad Cap Saga]

Curious George jorge234q at yahoo.com
Thu Aug 21 10:58:04 CDT 2008

[apologies, I haven't been watching this part of this thread]

--- On Thu, 8/21/08, der Mouse <mouse at Rodents-Montreal.ORG> wrote:

[attribution lost]

> > Don't get me wrong, I -like- that we're getting reliable high-speed
> > peripheral buses.
> It's fine to have them available.  Having no alternative is not fine.
> > However, there are a lot more folks who can go from "neat idea" to
> > "cute widget on the desktop" quickly via a parallel port versus USB.
> > For one thing, there are very few through-hole USB interfaces.
> For another, with a parallel port you don't need a clock and a
> specialized interface chip that's comparatively expensive and difficult
> to interface to without a CPU.  And you need a clock, probably up in
> the megahertz at least.
> Give me a nice simple breadboard full of TTL.  No clocks, no CPUs, no
> tri-state buses, no RAM or ROM.  I've got one such circuit in
> production use right now, controlling the relays I installed into a
> 12-outlet power bar.

I don't use the parallel port (my computers all sit on print servers)
so I don't know what the "modern" consequences of its absence are :<

But, can't you get a "USB printer cable" (USB connector on one end
and centronics connector on the other) and treat *that* as if it
were your printer port?

The potential problem I see there is you can't just push a nice
byte stream out an I/O port and have those values appear
sequentially on a set of pins -- you're now stuck going through
the USB driver (which at least solves *that* problem) and whatever
limitations it places on the sequencing of control pins (i.e., you
can't toggle any pin at any time, arbitrarily).

<shrug> Or, do these little cables take *all* that control away
from you?

Note that you can also easily fabricate a serial-parallel converter
and move this functionality to a conventional serial port (e.g.,
something akin to the 6402/1602... can't remember my part numbers).
Of course, nowadays, doing that would be simpler with a tiny

[of course, this only addresses low speed interfaces since you
are now crippling the available bandwidth even more than the parallel
port -- OK for flipping relays, *not* OK for parallel port optical
scanners, etc.]

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