The Link Electronics PCE-845 Closed Caption Encoder inserts closed caption/ text data on line 21 field 1. The unit will also insert on line 21 field 2 for extended data service. Channel one and channel two for caption or text are programmable through the software package. The video path has excellent differential gain and phase. The RS-232C is controlled through a 9 pin D connector. The input and output signals are baseband, Y/C and R-Y, B-Y, Y.