The physical interface PDA-100 allows direct logging of data via RS 232 interface by a computer, and subsequent fluorescence quenching analysis by the WinControl software. Also, the PDA-100 permits control of the internal drivers for the XE-AL Actinic-/Saturation Light Unit by the WinControl software. WinControl-commands, like ON/OFF of various light sources, are transmitted via a special remote control cable to the fluorometer. XE-PAM fluorometers with serial numbers > 0124 are already equipped with a corresponding connector. All other instruments can be easily upgraded..