公开(公告)号：DE2334566A1

公开(公告)日：1974-02-21

申请号：DE2334566

申请日：1973-07-07

Applicant: IBM

Inventor： STILWELL GEORGE R ,  WEISS ALFRED

IPC: H04J3/00 ,  H04J3/02 ,  H04J3/06 ,  H04L5/24 ,  H04L27/26 ,  H04Q1/457 ,  H04Q11/04

Abstract: Parallel tone signals received on a plurality of input lines are digitized. Specific tone combinations represent different data, such as a particular digit or character. A received signal is considered a valid data signal if it is of at least a predetermined minimum time duration. The digitized signals are read into individual shift registers for each line. The length of each shift register is sufficient to store two data signals, each of the predetermined minimum valid time duration. The tone signals received on the input lines are asynchronous and of variable time duration. A multiplexer sequentially reads out the storage registers at a rate which is relatively high compared to the rate at which the digitized signals are entered into the registers. The time-division-multiplexed serial samples from all registers are reconverted to the input tone signals, frequency separated and detected in a multi-frequency receiver, and then applied to a demultiplexer so that the detected signals appear on a plurality of output lines corresponding to the plurality of input lines. Even though each register is completely read out during each sample time by the multiplexer, the last half of the signal stored in a register is recirculated back into the register to be read out as the first half of the register's contents the next time the line is sampled by the multiplexer, thereby eliminating the possibility of the loss of a digit or character during the multiplexing process.