| 摘要 |
PROBLEM TO BE SOLVED: To provide an ADPCM coder that becomes capable of conducting a remote loopback based on instruction from a transmitter even through a transmission line without assignment of a control signal for a test instruction. SOLUTION: An ADPCM coder 10 at a transmitter side has a logic inversion circuit 12 that inverts the output logic of an ADPCM coder 11 with a logic ('0' is significant) of a control signal instructing signal loopback to an opposite party. An ADPCM coder 20 at a receiver side is provided with a zero data detection circuit 25 that detects the presence of a logic of the control signal in received ADPCM coded data, and a switching section 24 that provides the output of an ADPCM decoder 223 to an ADPCM coder 21, when the presence of the logic of the control signal is detected in the received ADPCM coded data. |
