Re: a USB for the Apple II smoke test

[David Wilson <david@uow.edu.au>]

The Wizard of Oz <wizard@emeraldcity.gov> writes:
>	Bad analogy. A better one would be like what a bison has to do with a
>cow. The hardware protocols can't be a lot different. After all there is a
>direct path from RS-232 to USB. I bought a couple of RS-232 to RS-232-C
>(25 pin to 9 pin) adaptors. Friends have bought RS-232-C to USB adaptors.
>None of these adaptors required circuitry. It was all a matter of wiring.

DB-25 to DE-9 (PC/XT to PC/AT style serial ports) is simply 9 wires joining
9 of the 25 pins. An RS-232C to USB adapter is not so simple.

Have a look at the FTDI website http://www.ftdichip.com/Products/FT2232BM.htm
for information on a chip designed for this purpose. Mice and keyboards
often come with simple PS/2 to USB adapters. These work because both PS/2
and USB supply 5VDC power and the keyboard/mouse microcontroller is programmed
to function in both PS/2 and USB modes depending on what they are plugged
into. RS-232 uses bipolar (-12 to -3V and +3 to +12V) signals and does not
provide the regulated 5VDC required by USB mice.
-- 
David Wilson  School of IT & CS, Uni of Wollongong, Australia