Importance

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Abstract

A microcomputer with an external bus interface for providing communication with external peripheral devices such as memory and the like is provided with on-board chip select logic and programmable bus stretching capability. The chip select logic provides chip select signals to external devices when addresses fall within pre-selected ranges, eliminating the 'glue' logic normally required for this purpose. The programmable bus stretching feature inserts a pre-selected number of 'wait states' into any external bus cycle for which it is programmed by stretching, or freezing, the central processing unit and external bus interface unit clocks. Other internal clocks, such as those which drive timers and/or serial interface baud rate generators are not frozen by the bus stretch.

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First Claim