Bob Ammerman wrote:
>
> It is actually outside the USB spec to make any 'extension cord' or overlong
> cable. For example a A-male to A-female or B-male to B-female cable are
> "illegal" because they could be used to make a connection that is too long.
>
> The design decisions made in the USB spec were intended so that no matter
> what you did, if you could hook something up, it would work. (The only

Yeah, right. Some crap driver s/w won't work even with a short cable!
(WaveX MP3 player for one).

> exception is that you could hook up a chain of more than five hubs, which is
> relatively unlikely to happen).

Happened at a Comdex demo of early USB. "Look how many USB devices we can
hook up". They supposedly made it out to 250 something before
the software broke. With the typical 4 port hubs of that day, that
would mean 3**5 =243 maximum devices.

> Another design decision involved having low speed devices requiring captive
> cables (or cables with a custom (non-USB connector) end at the device) that
> are not longer than a certain limit. I forget the details on this, but I do
> remember that it was a requirement to ensure reliable operation (otherwise
> the user could use a cable designed for full speed operation and get
> problems). And yes, low speed devices are limited to shorter cables than
> full speed devices because of the simpler signaling scheme used.

And yet they use type A connectors, for which extension cords are readily
available.

Part of the distance issue is that manufactures use the cheapest cables
they can get away with. Higher grade (low capacitance) cables
(as used on IEEE 1288 printer cables) extend the range markedly.

> Unfortunately idiotic companies don't follow the spec properly, leaving
> support folks to deal with the grief.

You're talking mostly about MicroSloth I presume...

Q: How many MicroSoft programmers does it take to change a light bulb?

A: NONE. They just define "Darkness" to be the new standard.


R

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.