Serial interfaces (was Re: Any former Psion 5 owners out there?)

Tony Duell ard at
Sun Jul 25 13:10:07 CDT 2010

> >> [USB dongles] work *remarkably* well with even old printers [...]
> >> but not any other parallel-port device, AFAIK.
> >
> > But there's nothing inherent in the USB spec that prevents this as a
> > possibility, its simply the kind of USB dongle that people have built
> > to date, right?
> I have no idea on technical grounds, but inasmuch as there are, or
> were, USB<=3D>SCSI adaptors, I think it's /technically/ possible in
> terms of electronic capabilities. What I suspect on no particular

I've enver seen the actual USB spec, but I can think of no reason why 
this is impossible.

Incidentally, is the USB spec -- a low level one describing just what 
goes on on the 2 signal wires, etc -- available anywhere, or would I have 
to sign NDAs, etc, to get it?

> evidence is that software-wise it probably isn't, 'cos I am /guessing/
> that a USB device can't present itself as a port on 0x378 on IRQ 7
> etc.

I can't think of any obvious way of trapping I/O instructions on an 80x86 
processor (which is essentially what you need for this). If you haf the 
specs of whatever device you were trying to link up, then I guess you 
could write drivers to use the USB adapter, but it would be a lot of work..

Incidentlaly, what do the USB-serial adapters do? I assume they don't 
respond to acesses to the I/O ports conentionally used for PC serial 


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