Some of the USB to serial adapters are a bit choosy or, I should say,
some applications can be choosy about the adapters they will talk to.
I've had good results with the unit that pfranc sold some years ago when
connecting to it from native C programs running under Linux, but Win95
apps running on Linux under Wine didn't want to know, even though they
worked just fine over a multi-port serial adapter card. I put that down
to the total lack of serial support provided by DOS or Windows 95 or
earlier. These simply let you access to bare metal UART, which I did via
a third party serial i/o library (Willies Software's COMM-DRV) but I
don't know how that would have interacted with a USB adapter and have no
idea what code the aforementioned applications I tried under Wine used
for serial access or where they got it from.
Another possibility would be to use an Ethernet to serial converter such
as:
- Lantronix Xport -
http://gridconnect.com/network-components/xport.html
- NEMO10 -
http://kanda.com/products/Sena/NEMO10.html
- LSHM-200 -
http://www.radi.com/modular64.htm
These are all component-level devices that would need to be mounted and
connected to the UART and a power supply. Or, you can find commodity
adapters on eBay among other sources: they are typically a plastic case
with an RJ-45 socket in one end and a D-9 serial connector in the other.
IMO these are a better bet than USB adapters because Java has built-in
TCP/IP support but probably can't talk to a USB<->serial adapter at a low
enough level to set baud rate, parity and stop bits correctly. The
Ethernet to serial converter module takes care of this because it
connects locally a UART and takes care of configuring itself to talk to
the serial port (UART): some can be hard-wired while others are
configured with a web browser and keep the configuration in flash memory.