CMOS implementation of a built-in self test input generator (BISTIG)

Claim 1

In a built in self test input generator (BISTIG) for a programmable logic array (PLA), wherein the PLA comprises a first level array adapted to receive N input signals in N input lines and to provide M product terms on M product term lines, and a second level array adapted to receive the M product terms on the M product term lines and to provide P output signals on P output lines, wherein N, M, and P are integers greater than one, the BISTIG having a product term selector which sequentially enables each of the M product term lines of the second level array individually in response to a first control signal, an improved test vector generator comprising: initialization means for selectively generating an initial N-bit vector comprising N-1 logical zeroes and a single logical one in response to a second control signal; N-stage, recirculating shift register means, coupled to said initialization means, for selectively generating one of N test vectors by sequentially shifting each of said N-bits comprising said initial vector by one bit in response to a third control signal; coupling means, coupled to said shift register means and to said N input lines of said PLA, for selectively coupling each of said N-bits comprising said one test vector to a corresponding one of said N input lines in response to a fourth control signal, thereby allowing said single logical one to be shifted across a true and a complement of said N input lines; and control means, coupled to said product term selector, to said initialization means, to said shift register means and to said coupling means, for receiving a test signal and each of a plurality of clock pulses, and selectively providing said first control signal each time said shift register means recirculates said logical one, thereby incrementing a product term address provided by said product term selector, and selectively providing said second control signal in response to first receiving said test signal, thereby initializing said product term selector to an initial value, and selectively providing said third control signal in response to receiving each clock pulse, thereby shifting said single logical one into one of said N-stages of said shift registers means, and providing said fourth control signal substantially continuously while receiving said test signal.