Abstract: A digital-based phase shift keying modulating device is disclosed. A phase code command signal is applied to an exemplary bi-phase shift keying modulating (BPSK) device designed in accordance with the present invention to phase reverse by 180.degree. the output signal produced by the device. The exemplary BPSK modulating device is capable of producing an output signal of either triangular or sinusoidal shape. A preferred embodiment of the exemplary device is implemented by using a single exclusive OR logic gate in conjunction with a frequency synthesizer, which is comprised of an accumulator, an output register, and a group of exclusive OR logic gates. The modulator device has a variety of applications in digital communication systems such as, for example, ground-based and spacecraft communication systems. The disclosed BPSK modulating device is particularly useful in spacecraft data link communications systems wherein weight, volume, and power consumption are at a premium.