Macomber loom controls come in two variations: 
Air-Dobby and ESP
(electronic single pedal).  These are direct replacements for the original Macomber power supply/loom control.  Connection to the computer is with an integral USB cable.

Electric Single Pedal (ESP)
Flatwater Electronics Main page
They have visual indicators showing both loom operation and communications between the loom control and the computer.  These indicators help to identify whether problems are with the loom or the computer.
The USB connection uses the FTDI USB to Serial.  With the latest versions of Windows and starting with Mac OS X 10 the Converter is "plug and play" as the USB drivers are included in those operating systems.  

For older systems, such as Windows XP or Mac OS X 9 and earlier, a driver may be downloaded to your PC and installation is straightforward.