Abstract: A digital processor based voiceband modem that provides computers and terminals access to telephone lines and performs line control functions to originate, answer and terminate data calls in addition to converting baseband signals to voiceband and voiceband signals to baseband. The modem utilizes a signal processor that executes various signal converting algorithms under control of selected sets of instructions and further utilizes a digital processor that executes line control algorithms for alternative modes (i.e., originate or answer) of the data modem. An outgoing or incoming call enables the appropriate mode and, during the execution of the corresponding line control algorithm, various sets of instructions are selected to execute signal converting algorithms appropriate for the enabled mode of a specific one of various data modem types.

Abstract: A Differential Phase Shift Keyed (DPSK) receiver is arranged to detect DPSK signals that contain the O.degree. vector as an information bearing signal in its constellation. The received signal is phase shifted by 90.degree.. A 45.degree. phase shifted signal is thereafter synthesized by additively combining the DPSK signal and the 90.degree. phase shifted signal. Using these signals, detection proceeds by means of correlation techniques. The polarities of the correlation products uniquely determine the phase changes of the DPSK signal.