Abstract: A circuit for resetting a computer upon detection of changes in the signals of an RS-232C communications port in the computer. The changes may indicate an incoming phone call or loss of a previously established communication link. The circuit may monitor the RING INDICATE (RI) signal of the RS-232C port to detect the former condition and either the DATA CARRIER DETECT (DCD) signal or the DATA SET READY (DSR) signal of the RS-232C port to detect the latter condition. A timer prevents spurious changes in the monitored signal from causing the computer to reset.

Abstract: A switching circuit places a load across the TIP and RING signals of a telephone line when the computer is reset and removes the load when the computer accesses a selected memory location. Thus, the telephone line remains in an off-hook state after the computer is reset and remains in that state until the computer executes software that causes the telephone line to return to the on-hook state. The computer may also execute software that causes the telephone line to enter the off-hook state.