My equipment:
Yaesu FT-857D
Donner Digital Interface
Dell Inspiron B120 laptop with a serial-to-USB converter plugged into
the USB port
Windows XP

From Windows XP, I go to Control Panel -> System -> Hardware -> Device
Manager and confirm that port COM4 is the one being used.

In DigiPan, I go to Configure -> Serial Port and select COM4 with PTS
and DTR as PTT. I'm able to transmit in PSK-31.

But under IZ8BLY, I'm unable to transmit anything. Even after closing
DigiPan, setting the mode to Feld Hell under the Mode menu, and
configuring File -> Preferences -> PTT to make COM4 the PTT control, I
STILL CANNOT TRANSMIT. What's wrong here?

With DTR only, I can transmit PSK-31 in DigiPan. In fact, as long as
RTS is unchecked, the transceiver is stuck in transmit mode. So it
apparently means that the DTR line is in use.

I downloaded and installed the program from
http://www.driverlinx.com/DownLoad/DlPortIO.htm

But I have NO idea how to proceed once I have the DlPortIO program
installed.

PLEASE don't tell me to read the official documentation. I did so
again and again and again to no avail. I need EXPLICIT instructions
on what to do.

I REALLY need to be operational on Feld Hell. I've been stuck in a
rut as an amateur radio operator. I have lots of unfinished projects.
I need to COMPLETE SOMETHING for once. Feld Hell is just so
tantalizingly close for me.