Maximum length pseudo-random test pattern generator via feedback network modification
First Claim
1. An exhaustive test pattern generator for generating 2n test patterns, comprising:
- (a) feedback shift register means comprising a feedback network logically coupled to only a single input of a shift register for generating a sequence of 2n -1 test patterns;
(b) means external to the feedback shift register means for generating a 2n th test pattern and for inserting the 2n th test pattern into the sequence of 2n -1 test patterns; and
(c) output means for providing the sequence of 2n test patterns.
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Abstract
A system and method for generating 2n test patterns is disclosed. The system utilizes a linear feedback shift register (LFSR) to generate a sequence of 2n -1 test patterns. In addition, the system includes apparatus external to the shift register which generates a 2n th test pattern. A switching circuit is employed to insert the 2n th test pattern into the sequence of test patterns. Therefore, a 2n test pattern sequence is generated. The test pattern sequence produced is pseudo-random in nature. The system further includes an output for providing a test pattern; such output could be used for the testing of a very large scale integration (VSLI) sub-system such as read only memory (ROM). A method utilizing the techniques embodied in the system is also disclosed.
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Citations
27 Claims
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1. An exhaustive test pattern generator for generating 2n test patterns, comprising:
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(a) feedback shift register means comprising a feedback network logically coupled to only a single input of a shift register for generating a sequence of 2n -1 test patterns; (b) means external to the feedback shift register means for generating a 2n th test pattern and for inserting the 2n th test pattern into the sequence of 2n -1 test patterns; and (c) output means for providing the sequence of 2n test patterns. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A test pattern generator for generating 2n test patterns, comprising:
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(a) shift register means for storing a series of test pattern signals as a test pattern; (b) feedback network means logically coupled to an output of the shift register means for generating a sequence of 2n -1 test pattern signals; (c) circuit means logically coupled to an output of the shift register means for generating a 2n th test pattern signal; (d) switching means logically coupled to the shift register means, the feedback network means and the circuit means for inserting the 2n th test pattern signal into the sequence of test pattern signals generated by the feedback network means and for serially providing the sequence of 2n test pattern signals to only a single input of the shift register means; and (e) output means for providing the sequence of 2n test patterns. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method for generating 2n test patterns for use in exhaustive testing, comprising the steps of:
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(a) checking a selecting signal for a "true" or a "false" signal; (b) if the selecting signal is "true", generating with a feedback shift register device comprising a feedback network logically coupled to only a single input of a shift register one of 2n -1 possible test patterns; (c) if the selecting signal is "false", generating with means external to the feedback shift register device a 2n th test pattern not included in the 2n -1 possible test patterns generated by the feedback shift register device; (d) outputting the test pattern to an external element; (e) feeding back the outputted test pattern through the feedback network; and (f) repeating steps (a) through (e) to generate an exhaustive test sequence of 2n unique test patterns. - View Dependent Claims (24, 25)
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26. A test pattern generator for generating 2n test patterns, comprising:
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(a) shift register means comprising a plurality of bistable multi-vibrators logically coupled in series from an output signal of a first bi-stable multi-vibrator to an input signal of a second bi-stable multi-vibrator for storing a series of test pattern signals as one of 2n test patterns, the plurality of bi-stable multi-vibrators including initializing means for setting the initial test pattern signals stored by the bi-stable multi-vibrators so that the shift register means can be set to a predetermined test pattern at the beginning of test pattern generation; (b) feedback means comprising combinational logic logically coupled to a plurality of output signals form the bistable multi-vibrators for generating an XOR function of the output signals and for providing to an output the generated function as one of a sequence of 2n -1 test pattern signals so that a sequence of 2n -1 unique test pattern signals is generated; (c) circuit means logically coupled to one of the output signals of one of the bi-stable multi-vibrators in the shift register means for providing to an output the 2n th test pattern signal; (d) switching means for inserting the 2n th test pattern signal provided by the output of the circuit means into the sequence of signals generated by the output of the feedback means so that a sequence of 2n test patterns is generated and for serially providing the sequence of 2n test pattern signals to only a single input of the shift register means; and (e) output means logically coupled to at least one of the bi-stable multi-vibrator outputs for providing the sequence of 2n test patterns. - View Dependent Claims (27)
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Specification