| 摘要 |
PURPOSE:To obtain a modulator-demodulator not requiring manual operation for loopback by detecting/discriminating loopback data transmitted from the central side regardless whether the system is the full duplex communication system or the half-duplex communication system and looping back automatically the data. CONSTITUTION:Data received from a terminal 20 of a central side modulator- demodulator 3 is stored in a register 12 and transmitted to a discrimination control circuit 16 at the same time. The discrimination control circuit 16 uses a loopback control data 24 transmitted from the register 12 to discriminate whether or not the test is a loopback test, whether the system is the full duplex communication system or the half-duplex communication system and a loopback point in case of the loopback test. The loopback test data transmitted to a changeover swtich 13 is transmitted to a modulation circuit 14. The loopback test data modulated by the modulation circuit 14 is looped back via changeover switches 15, 19 switched by changeover switch control signals 27, 28 transmitted from the discrimination control circuit 16 and transmitted to a demodulation circuit 18. |
