Okay, here goes. Once upon a time there was just serial and gpib. Each used completely different hardware,protocols, etc. and there were separate drivers for each. Years ago, a new instrument type was introduced. Based on a VME backplane, these were instruments on a card called VXI (VME with instrument extensions). So, a whole new low level driver was required. The makers of VXI, realizing that the first VXI instruments were the same as their GPIB instruments without a display or power supply, thought that it would be nice if the software that had been developed for the GPIB instruments could also be used for the VXI version. Several vendors, including NI, came up with something called VISA (Virtual Instrument Software Architecture). This was an API that united GPIB and VXI. If you wrote an instrument driver with VISA Writes and VISA Reads, it would work with either type of instrument. The VISA driver itself would determine the actual type of bus and handle all of the low level details. One of the goals of all these vendors was to also make it easy for users to change from GPIB to VXI instruments. While this didn't really happen, the idea of VISA caught on and became very popular and sort of a standard in many places. Eventually, other common forms of instrument busses were added to VISA. Among those are serial, ethernet, usb, pxi. All of the instrument drivers written by NI now use VISA.
I downloaded the driver for the instrument you need and had a look at it. It really doesn't have much, it's very old, and uses the GPIB functions (not VISA). Since there were so few functions, I went ahead and replaced the GPIB Reads and Writes with VISA Reads and Writes. That will give you a start. You will also need to add some code to initialize the serial port. A great place to look to see how this is done is with an example that has shipped with LabVEIW for years. The HP34401 DMM driver that is on the instrument driver palette is a VISA driver with special support for serial. All of the serial setup is done in the initialize subVI. The type of interface is determined and if serial, baud rate, parity, etc. are setup. Another important setting is a termination character. Serial instruments usually require a CR or LF at the end of each command. You will need to determine what your instrument requires.
