I did some work on the Linux serial device driver for the Prolific PL2303 and it can certainly do low bit rates. https://github.com/torvalds/linux/blob/master/drivers/usb/serial/pl2303.c

On Linux you can set an arbitrary rate (but only to the whole baud) but if you modify the drive you can get a little closer (45.77 Bd).

I plugged the device I have here into a windows 10 machine and it allows a 75 Bd rate (which is one of the 'standard' rates) but I don't think the Prolific driver will do arbitrary rates.

USB to Serial cables with the PL2303 are cheap on Amazon ($10) (mine is made by Sabrent).

cheers,

    Michael (NV3Z /VK2BEA / G4NYV)

On Wed, Mar 9, 2022 at 8:25 PM Jeff Stai <wk6i.jeff@gmail.com> wrote:

I want to connect and use my ancient but beloved hardware modems via an RS232 to USB connection. 

I have dodged this question for years by installing PCIe to RS232 adapters that were 16550 UART compatible. These adapters go slow enough to transfer 45/75 baud.

Modern FTDI USB/RS232 adapters won't go below 300 baud. And I'm running into needing to connect to Win10/Win11 PCs that don't have available PCI slots. (Progress...)

I know old Edgeport adapters might be the answer. If I can find one and the available drivers behave on Win11 maybe that will work... but are there any other alternatives I'm missing?

Thanks & 73 jeff wk6i

--

Jeff Stai ~ WK6I ~ wk6i.jeff@gmail.com

RTTY op at W7RN

Twisted Oak Winery ~ http://www.twistedoak.com/