Abstract: Input and output fault monitoring circuits for determining the presence of integrated circuit chip open connections at the input and output pads of each circuit on a chip. The input fault monitoring circuit operates on the principle that if there is no input signal from the input pad throughout the known duty cycle or frequency of the input circuit, a defect, such as an open circuit interconnect, has occurred. The output fault monitoring circuit generates a signal through a dummy circuit connected to the output circuit which has a time delay intermediate that of the output circuit operating into a connected output pad and that of the output circuit when operating into a disconnected pad. Thus, the time of arrival of the dummy circuit signal in relation to that of the actual output signal is used to indicate the presence or absence of a disconnected output pad.

Abstract: Apparatus for use in a signalling system for communicating with a centralized communication center over a telephone network. The signalling system includes apparatus operative under prescribed circumstances to produce an alarm condition for initiating an alarm communication by which alarm data can be communicated to the centralized communication center over the telephone network, and apparatus operative at a prescribed time of day to produce a self-check condition for initiating a self-check communication by which prescribed data can be communicated to the centralized communications center over the telephone network. The apparatus in accordance with the invention includes a programmable read only memory which stores telephone number data representing first and second telephone numbers, and a microprocessor which utilizes this data in attempting communication with the centralized communications center.