| 摘要 |
PURPOSE:To enable timing switching automatically by a modem itself at loop test in multiplex network of cascade connection by devising a modem adjacent to a modem being a component so as to apply the switching of a timing signal source. CONSTITUTION:Each modem is provided with a means A storing a direction where a self-timing signal source exists and a means B storing the identification signal of a modem adjacent to its own modem and the modem uses a timing signal source switching means C in the modem so as to discriminate whether or not a self-oscillation timing signal source is included in the test loop and when no source is included, the other oscillation timing signal source of the modem is switched into its self-oscillation timing signal source. Thus, since each modem switches the timing signal source from the other oscillator to its self-oscillator automatically in the loop test of a data transmission circuit in this way, the loop test is conducted smoothly and efficiently. |
