Pulse code modulated digital telephony tone generator

摘要

A tone generator is disclosed comprising an LSI controller and read only memory to provide any one of a pre-established set of audio signals to a standard pulse code modulated data stream. This is accomplished utilizing the origination address and destination address that appear on the origination and destination buses in every cycle of data. The origination address designates any one of the pre-established signal patterns stored in the ROM. The designated signal is read onto the data bus by the disclosed signal generating system by reading out the elements of the signal tone stored in the ROM. The predefined tones are stored continuously and regenerated continuously by the controller; thus, each tone is available during each frame cycle to be read out when the origination address calls for the tone. The samples of the tones and signals are stored in the ROM in the digital form they will have on the PCM data bus. The destination address defines the point to which the designated tone signal will be transferred. It is only necessary to store enough data for each signal to complete one nonrepeating cycle; the first 64 words (2 bytes each) in the ROM designate the number of samples stored for each signal so that the controller knows where signal table starts in the ROM. Transmission of a complete tone is accomplished in the LSI controller's circuit by incorporating a counter therein which increments the address of each tone every frame, and stores it on the chip RAM to be retrieved in the next frame to read the next of the sample of the tone. As the controller senses the predefined end of each tone, the counter is reset to the starting address of that particular tone. The instantaneous value of each tone is stored in an output register in the controller to begin transmission of the tone immediately if an origination address or addresses request it. Several tones can be addressed simultaneously within the same time frame, and the tone addressed by the controller can be varied every 488 nanoseconds with the sample sent to a different destination.