What is a null modem?
The cable that connects the Impulse Laser Rangefinder to the iPAQ consists of four separate pieces. First is the serial cable that transmits data from the Impulse. The Impulse Laser itself is connected to the Impulse MapStar Compass via a serial cable with proprietary fittings (circular with 4 pins). A second serial cable attaches to the MapStar compass. This cable has an Impulse proprietary fitting at one end and a standard 9-pin serial connection at the other. A serial cable is also necessary at the iPAQ end. This cable attaches to the iPAQ serial port using the iPAQ proprietary connector and also has a standard 9-pin serial connection at the other end. These cables can be purchased, if lost, from Impulse and Compaq/HP, respectively. Although these two cables will directly connect to one another, the pin order from the Impulse to the iPAQ needs to be switched. This is done with a 9-pin null modem adapter. This adapter can be picked up at any Radio Shack for a few dollars. Often the n
