在许多遥测与保安设备中,调制解调器的连接可自动建立在两个系统之间。如果一个系统发生故障就能中断数据交换,虽然此时调制解调器的连接仍然有效,但是这种中断可要持续到工作人员把实际电路断开,或重新启动故障系统之时才停止。当我们在进行长时间的Internet下载操作时PC机突然发生事故,也会出现这种情况。为了避免这种故障,图1所示电路可以连续监控RS-232C数据线(TxD和RxD),并在检测到系统长时没有发送或接收数据 In many telemetry and security equipment, modem connections are automatically established between the two systems. If one system breaks down, the data exchange can be interrupted. Although the modem connection is still active at this time, the interruption can take place until the worker disconnects the actual circuit or restarts the failed system. This is also the case when a sudden PC accident occurs while we are doing Internet download for a long time. To avoid this failure, the circuit shown in Figure 1 can continuously monitor the RS-232C data lines (TxD and RxD) and does not send or receive data for long periods of time