| 摘要 |
PURPOSE:To prevent a phase locked oscillator from being oscillated by allowing a switching circuit to switch a clock from an N system into an E system with a loopback control signal at the loopback control. CONSTITUTION:A switching circuit 32 usually selects the clock of the N system and gives it to a phase locked oscillator 33. In this case, loopback is formed at the input section of a multiplex/demultiplex circuit 30 at loopback control because of the connection of input and output lines. On the other hand, the switching circuit 32 selects the E system clock from the N system with a loopback(LB) control signal. Since no clock loop through a clock path is formed at loopback, the oscillation of the phase locked oscillator 33 is prevented. |
