Bi-directional communication link for language teaching - includes programmed frequency sequencer generator for instruction encoding and shift register connected to frequency encoder

摘要

The system includes an instruction coding stage comprising a programmed frequency sequencer-generator (SG). This unit has an output signal (34) connected to the transmission line (36) and a control output (37) connected to the control input (38) of a shift register (RDE). The control inputs are connected to the outputs (41) of a frequency coder (CF). The inputs of the coder are connected directly to specific outputs (QO-Q4,Q9) of the shift register. Other coder inputs are connected to the remaining outputs (Q5-Q8) of the register via a stage (C) which combines them with the outputs of a control desk (P). The frequency coder (CF) comprises comprises a matrix of diodes. A detector (DO) senses the appearance and disappearance of commands and is connected both in parallel with the control desk outputs, and to control input of the frequency sequencer-generator.