Dave W wrote:


Paul, thanks for your input.

My USB converter is sold as a USB to parallel port converter - I have
to plug it into my Centronics cable to feed the printer. I can't find
any unidirectional converters online.

However perhaps my converter is only configured as a printer driver,
as why else would it display "no printer attached" if the port is for
general use? I have a USB to serial converter which shows as a COM:
port when plugged in, but my USB to parallel converter doesn't show as
an LPT: port.

My laptop has no facility for plug-in cards.

I didn't notice the Windows Update for more printers, so thanks for
mentioning it. I've tried it now but my printer isn't on the list.
Neither is the AGFA printer that would be accepted by my Canon.


I tried a few generic searches, and Google was its usual helpful self.

I tried tracing a hardware example, and I got a bit more traction that way.
The Prolific PL2305 is apparently a chip used in these USB cables.

https://www.startech.com/Cards-Adapt...5~ICUSB1284D25

"When this cable is installed correctly in Windows 10,
it will appear as USB printer support in the device manager,
not a standard LPT port."

And Windows would use a generic "USB Class" driver. I've been
trying to figure out what the class number is for that,
without success.

Now, I'll grab a manual for theirs. It uses a Prolific PL2305.

https://sgcdn.startech.com/005329/me..._NewManual.pdf

Using the chip number, this manual has a few pictures of
what Device Manager should show. This is a bit more useful
to your situation. There's still a gap though, as to whether
Device Manager knew right away (from a PNP perspective),
what was on the cable.

https://prolificusa.com/app/uploads/...tion-Guide.pdf

USB Root Hub
USB Printing Support
EPSON LQ-300+ /II ESC/P 2

When the EPSON driver is installed, there is an "Enable Bidirectional Support"
on what they call a Virtual Printer Port, but that won't be exposed for you
to tick right away.

I mean, if PNP is to work here, the interface pretty well has to be
flipped to Bidirectional by Windows.

And what I've read on this topic in the past, the claim was
that the driver "only supported one of four operating modes".
I've never seen a more detailed analysis than that, such
as someone checking with an oscilloscope, what modes
or pulse patterns it might be using. I think the reference to
the driver being "only a Printer driver", was to stop people
from trying to run their little hardware projects from that
cable. Not every hardware feature needed is exposed that way.

Paul