Abstract: An interface between a host computer and a crossbar switch is provided which employs data buffering using multiple-port RAM devices. The receive and transmit data is clocked into or out of separate serial ports of the RAM, and at the same time a local processor can access the RAM by a random access port, asynchronous to the serial ports, to execute the protocol. The order of storing bursts of data in the multiple-port RAM is defined by a free buffer manager which keeps account of which locations are free. The addresses of these locations are moved to a received list after being used for incoming packets. After the protocol processor has finished with its tasks, these addresses, referred to as burst data descriptors, are moved to a transmit list to await loading of burst data back to the serial registers for clocking out, then when transmitted the descriptors are again entered into the free buffer manager.

Abstract: A video imaging device coupled to a host computer by a communication line over which control data is transmitted, to one or more sources of video information, and to a monitor by a video line over which video signals based upon the video information and control data are transmitted, includes a converting unit for converting the video information into the video signals for transmittal to the monitor. A receiver receives the control data transmitted over the communication line. The control data includes condition data and associated instruction data with at least some of the instruction data being adapted to alter at least some of the condition data upon execution of the associated instruction data. Stored condition data may be selected in response to user generated event data and display of the video signals on the monitor is manipulated by execution of the instruction data associated with the selected condition data.