Importance

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Abstract

A system for testing an integrated circuit, and particularly a gate array, is disclosed which includes, prior to coupling the array to form a user-designed circuit, predesigned logic that enables testing of the user-designed circuit. The predesigned logic allows logic blocks in the array to operate in 'freeze' mode or to operate in normal mode, where normal mode is defined by the user-designed circuit. Much of the same circuitry in the logic blocks is, in fact, used in both modes of operation, thus minimizing circuitry added due to test. When the logic blocks are selected to be frozen, the logic blocks behave as a series of daisy-chained master-slave flip-flops. Stimulus data is shifted into the array and captured data is shifted out of the array through the daisy-chained flip-flops. Nonetheless, when data is shifted into and out of the daisy-chained flip-flops, the master latch and the slave latch of each flip-flop can be set to receive independent values and the data captured by each of the master and slave latches can be independently shifted out and analyzed. Although when frozen, the logic blocks behave as daisy-chained flip-flops, use of the logic blocks for testing purposes does not depend upon placement of sequential elements in the user-designed circuit in the logic blocks. In other words, in normal mode, a logic block can implement combinational, sequential, or other functions and still later be used to drive out stimulus values or capture results. Moreover, each logic block is further equipped for addressable mode control, allowing selected logic blocks to be exercised in isolation once stimulus data is shifted in, simplifying test generation and improving fault coverage. Using a logic block in accordance with the invention results in a high level of fault coverage, while placing few limitations on the user's circuit design.

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First Claim