Abstract: An interface circuit for providing asynchronous interrupt service for multiple peripheral devices in accordance with instructions from a host computer includes two dual universal asynchronous receivers-transmitters ("UARTs"), a dual port random-access memory ("RAM") and a microprocessor (".mu.P"). The dual UARTs selectively read data separately from selected peripheral devices and selectively write that data to the dual port RAM for access by the host computer, and read data from the dual port RAM as stored therein by the host computer and write that data to a selected peripheral device, in accordance with addresses from the .mu.P. Following initiation of an interrupt sequence, the dual port RAM allows the host computer to selectively and asynchronously read data (e.g. from a peripheral device via a dual UART) therefrom and write necessary data or instructions (e.g. for the .mu.P or a peripheral device via a dual UART) thereto for the .mu.

Abstract: A self-contained, computer controllable, video synchronization and frame pulse signal generator for generating a video synchronization signal, such as video black burst, and a video frame pulse signal indicating the presence of a video signal frame. The present invention can be connected as a subsystem within an existing personal computer having an open architecture (e.g., as a plug-in interface board in a PC-AT.RTM.). The video synchronization signal is useful as a master synchronization signal source within a video signal processing system (e.g., an off-line video editing system). The video frame pulse signal is synchronized to the video synchronization signal and can be selectively gated under computer control to produce an interrupt signal useful as a stimulus for a computer's software interrupt routines within a video signal processing system.

Abstract: A system for testing digital circuitry includes a signature generator that is connected to a plurality of nodes in the circuit to be tested and that generates signature words unique to identical streams of binary data signals or clocking signals. A multiplexer sequentially directs streams of signals to the signature generator from selected test nodes, or data streams from a plurailty of nodes can be signaturized simultaneously.