Abstract: A system for automatically time setting and message setting or programming of a cased digital watch or a watch module and including both an external setting unit and a serial interface control circuit inside the cased digital watch. The system in accordance with the invention is compatible with either watches that require time setting or watches that require both time setting and message programming and is applicable to any type of manually controllable watch. The time and message set system has a data entry unit that includes a keyboard, a display, a reference time module, a memory, a light source such as a light emitting diode or an LED array as an output and a processor which provides central control of the other functional units. The LED array output supplies coded messages to a light or energy responsive device or phototransistor in position under the face of the watch. The watch includes a novel circuit for responding to the phototransistor and provides time setting and message setting.