Tone signal generator for time multiplex telephone exchange - reads out stored waveform samples under stored instruction control, incremented after each tone cycle (BE 12.12.80)

摘要

In a time division multiplex telephone exchange, tone signals are supplied by a digital signal generator. Each tone frequency is stored as a sequence of 8-bit words representing successive samples of one cycle. They are read out, one at a time, and sent in the appropriate time channel by a logic instruction circuit. Specifications for signals, e.g. a 4-tone signal, are stored as sets of 4 words and are read out by the logic circuit, controlled by a clock driven channel selector. The generation of a signal is monitored by a word stored in a transmission control store. It is incremented after each cycle of tone and compared with the specification to control duration of tone, spacing and switching to next frequency. Sixteen such signals are generated continuously and sent in different time channels.