Broken wire detection within a security surveillance network

An electronic communications network system including an electronic communications device and an expander device communicatively coupled via a first differential half-duplex communications bus to and upstream from the electronic communications device, the electronic communications system expander device including a differential receiver, an electronic processor, and a broken wire detection circuit including a load resistor selectively connectable to an input of the broken wire detection circuit, the broken wire detection circuit being communicatively coupled at the input to the first differential half-duplex communications bus and communicatively coupled at an output to the electronic processor, wherein the electronic processor is configured to:

• transmit a first message over the first differential half-duplex communications bus to the electronic communications device;
• detect, at the differential receiver, a response message over the first differential half-duplex communications bus from the electronic communications device;
• connect, in response to detecting the response message, the load resistor to the input of the broken wire detection circuit;
• disconnect, during reception of the response message from the electronic communications device, the load resistor from the input of the broken wire detection circuit;
• determine, based on a signal from the broken wire detection circuit, whether a broken wire condition exists within the first differential half-duplex communications bus;
• and
• generate, in response to determining that the broken wire condition is present, an alert to a user.

A method of detecting a broken wire condition of a first differential half-duplex communications bus, the method comprising:

• transmitting, from an electronic communications system expander device, a first message over the first differential half-duplex communications bus to an electronic communications device connected downstream from the electronic communications system expander device;
• detecting, at a differential receiver of the electronic communications system expander device, a response message over the first differential half-duplex communications bus from the electronic communications device;
• connecting, in response to detecting the response message, a load resistor of a broken wire detection circuit of the electronic communications system expander device to an input of the broken wire detection circuit, the broken wire detection circuit being connected to the first differential half-duplex communications bus at the input;
• disconnecting, during reception of the response message from the electronic communications device, the load resistor from the input of the broken wire detection circuit;
• determining, based on a signal from the broken wire detection circuit, whether a broken wire condition exists within the first differential half-duplex communications bus;
• and
• generating, in response to determining that the broken wire condition is present, an alert to a user.