On 9/11/05, Tom Gal <[EMAIL PROTECTED]> wrote:
> > I can think of three reasons.
> > 1) the USB cable end is externally symmetric, usually without any
> > orientation markings.
> > 2) the USB chassis end (A connector) is externally symmetric
>
> I'm not really sure how to interpret that because the A connectors
> (plug in to your comp or whatever USB Host) always have the USB symbol
> facing up. As for the other end the full size connectors have rounded
> edges and the commonly used mini connectors are even more oddly
> shaped. Are you talking about not the cable but the ports themselves?
> I'm not saying it doesn't happen to me (impatiently trying to plug
> something in while multitasking), but if you use any device enough to
> run into the problem, it's likely if you look at the cable it's not a
> problem.
Which way is "up"? 2/3 of the computers that I use have connectors
mounted with the USB receptacles vertical, and on the back panel
besides. Several of the USB cables that I own do not have any marking
on the A connector.
> > It would have been better to use hermaphroditic connectors, like the
> > GR 874 RF connectors.
>
> I'm not sure what those are, but I'm guessing they didn't care power
> on the same bus
They were RF coaxial connectors, but the principle is the same.
> Unlike many household appliances most embedded
> devices are not built with extra circuitry to handle reversed
> polarity.
Nowadays most household appliances seem to come with polarized
two-conductor plugs.
Connectors can be designed to transmit the same polarity no matter
which way they are plugged in. It gets fairly complicated if there
are more than 4 connections, but fortunately that is all that is
required for USB.
You can read about this by a Google search keywords: jef raskin
hermaphroditic connectors
I can't find a picture online, so you will have to scare up a copy of
his book _The Humane Interface_.
carl
--
carl lowenstein marine physical lab u.c. san diego
[EMAIL PROTECTED]
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