Patent ID: 6278729
Filing Date: 2001-08-21
Classification: H04L

Abstract:
A method for testing a modem for connection to a telephone network line, comprising:comparing a voltage on a modem input adapted for connection to the telephone network line to a threshold voltage equal to or lower than a dial tone voltage by:connecting a first modem input conductor of the modem input to a first input of an operational amplifier;connecting a first resistor between an upper power supply voltage and a second input of the operational amplifier;connecting a second resistor between a lower power supply voltage and the second input of the operational amplifier, wherein the first and second resistors are sized to create a voltage drop across the second resistor equal to the threshold voltage;connecting a second modem input conductor of the modem input to an end of the second resistor connected to the lower power supply voltage;connecting an output of the operational amplifier to a Schmidt trigger; andemploying an output of the Schmidt trigger as a result of comparing the voltage on the modem input to the threshold voltage; anddetermining whether the modem has an electrical connection to the telephone network line based on the voltage on the modem input.