Abstract: A dual function readhead for a reflectance instrument is located in a housing for the instrument. A first light source for emitting radiation for reflectance readings and transmitting data is mounted in the readhead. In addition, a first photodetector is mounted in the readhead for detecting or receiving reflectance readings. A format or interface access port is defined in the readhead. An interface is provided that includes a second photodetector for detecting data transmitted by the first light source. A microprocessor is also provided for decoding data received by the second photodetector. A second light source may also be included with the interface for transmitting commands or data to the first photodetector. Software for controlling the operation of the first light source and the first photodetector is also provided.