Method for increasing the resolution of a digital fault dictionary

A method for determining a failed device in a unit under test, said method using a fault dictionary, said fault dictionary containing hard fault detection data and possible fault detection data, said method comprising the steps of:

• generating a plurality of fault syndromes, each of said fault syndromes corresponding to a primary output from a said unit under test, said unit under test being connected to an automated test instrument, said automated test instrument having a clock pulse generator for generating clock pulses, said automated test instrument executing a plurality of test cycles, each said test cycle including application of a plurality of test vectors to said unit under test said step of generating being effected by performing at least one of the following strategies, said strategies being selected by an operator of said automated test instrument:
• (a) executing a complete said test cycle;
• (b) stopping said test cycle when a first said failure of said unit under test occurs;
• (c) applying, to said unit under test a random number of said clock pulses between said test cycles;
• (d) performing step (c) between iterations of step (a);
• (e) performing step (c) between iterations of step (b);
• (f) performing step (c) between an occurrence of step (a) and step (b);
• in response to the situation wherein all of said fault syndromes are the same, using only said hard fault detection data in said fault dictionary to determine said failed device;
• and
• in response to the situation wherein at least one of said fault syndromes is different from any other of said fault syndromes, using only said possible fault detection data in said fault dictionary to determine said failed device.

A method for determining a failed device in a unit under test, said method using a fault dictionary said fault dictionary containing hard fault detection data and possible fault detection data, said method comprising the steps of:

• generating a plurality of fault syndromes, each of said fault syndromes corresponding to a primary output form a said unit under test said unit under test being connected to an automated test instrument and a power supply, said automated test instrument executing a plurality of test cycles, each said test cycle including application of a plurality of test vectors to said unit under test, said step of generating being effected by performing at least one of the following strategies, said strategies being selected by an operator of said automated test instrument:
• (a) executing a complete said test cycle;
• (b) stopping said test cycle when a first said failure of said unit under test occurs;
• (c) cycling said power supply between said test cycles by shutting off said power supply and then turning on said power supply;
• (d) performing step (c) between iterations of step (a);
• (e) performing step (c) between iterations of step (b);
• (f) performing step (c) between an occurrence of step (a) and step (b);
• in response to the situation wherein all of said fault syndromes are the same, using only said hard fault detection data in said fault dictionary to determine said failed device;
• and
• in response to the situation wherein at least one of said fault syndromes is different from any other of said fault syndromes, using only said possible fault detection data in said fault dictionary to determine said failed device.

In an automated test instrument using a fault dictionary and a plurality of fault syndromes to diagnose a failed device in a unit under test, said test instrument applying a plurality of test vectors in sequence to said unit under test, each said fault syndrome having indicia corresponding to a failed said primary output on said unit under test, a method for using possible fault detection data in said fault dictionary to determine a failed device in said unit under test comprising the steps of

• in response to the situation wherein all of said fault syndromes are the same, using only said hard fault detection data in said fault dictionary to determine said failed deice;
• and
• in response to the situation wherein at least one of said fault syndromes is different from at least one other of said fault syndromes:
• (a) determining the lowest test vector number in which a failure occurred during said application of said test vectors to said unit under test;
• (b) merging into a first combined fault syndrome, all of said indicia for each of said fault syndromes having the test vector number determined in step (a), said first combined fault syndrome thereby containing only one occurrence of each different one of said indicia;
• (c) accessing only said possible detection data in said fault dictionary using said failing pins in said first combined fault syndrome to determine a first failed device list containing at least one potentially failed device;
• (d) for the situation wherein more than a predetermined number of said potentially failed devices are present in said first failed device list, if a said fault syndrome exists in said fault dictionary having a higher said test vector number than the previous test vector number used to access said fault dictionary then merging into a second combined fault syndrome, all of said indicia for each of said fault syndromes having a next said higher said test vector number;
• (e) accessing only said possible detection data in said fault dictionary using said failing pins in said second combined fault syndrome to determine a second failed device list containing potentially failed devices;
• (f) creating a new first failed device list by taking the intersection of said first failed device list and said second failed device list;
• and
• (g) repeating steps (d) through (f) until the number of said potentially failed devices present in said first failed device list is not greater than said predetermined number.