Use a Prologix GPIB-to-USB Controller via Linux

Plug'n'Play on Linux

Plug the Prologix GPIB-USB Controller in on your Ubuntu 11.04 machine (most probably it will work on most older versions too) it directly shows up as a serial port via USB, such as /dev/ttyUSB0. No additional drivers needed. Here is the output of dmesg when you plug it in:

usb 2-2: new full speed USB device using uhci_hcd and address 5
hub 2-2:1.0: USB hub found
hub 2-2:1.0: 7 ports detected 
usb 2-2.1: new full speed USB device using uhci_hcd and address 6
ftdi_sio 2-2.1:1.0: FTDI USB Serial Device converter detected
usb 2-2.1: Detected FT232RL
usb 2-2.1: Number of endpoints 2 
usb 2-2.1: Endpoint 1 MaxPacketSize 64
usb 2-2.1: Endpoint 2 MaxPacketSize 64
usb 2-2.1: Setting MaxPacketSize 64
usb 2-2.1: FTDI USB Serial Device converter now attached to ttyUSB0


You simply have to use the serial interface and read / write data to the port.
As GPIB is a bus, devices have addresses. A serial RS232 connection is just a communication between two devices (so no addresses). If you want to forward data to a GPIB device, you must therefore specify the address of the device you want to talk to explicitly. This is done by sending the Prologix controller the special command ++addr x to tell it that the next commands go to GPIB device x. After having sent that statement you can send whatever you want the GPIB device to receive.