Abstract:
An apparatus for processing failure information received from a node of a circuit under test. The apparatus includes a fail processor which receives test data from a node and generates failure data based upon the test data, a plurality of fail memories, each memory being configured to receive and store certain fail data, and a sequence memory configured-to store sequence information indicating in what order the failure data is stored in the plurality of fail memories.

Description:
This application is a continuation of application Ser. No. 861,758, filed Apr. 1, 1992 now abandoned, which is a continuation of application Ser. No. 494,601, filed Mar. 16, 1990. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to fail processors. 
     It is known to generate patterns which are used in automatic test equipment by providing a high speed pattern generator which generates address sequences which are sent to a plurality of local generator circuits. Each local generator circuit includes a high speed local memory, a multiplicity of timing generators, a multiplicity of corresponding interpolators, a high speed formatter and a high speed fail processor. The timing generators and interpolators run in an interleaved fashion, with one timing generator/interpolator set receiving and generating all even cycle information and the other set receiving and generating all odd information. 
     SUMMARY OF THE INVENTION 
     It has been discovered that providing a fail processor which receives test data from a node and generates failure data based upon the test data, a plurality of fail memories, each memory being configured to receive and store certain fail data, and a sequence memory configured to store sequence information indicating in what order the failure data is stored in the plurality of fail memories provides an apparatus for processing failure information received from a node of a circuit under test. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The attached drawings illustrate the preferred embodiment, the structure and operation of which is then described. 
    
    
     DRAWINGS 
     FIG. 1 is a schematic-block diagram of a test system according to the present invention. 
     FIGS. 2-4 are examples of-how failure information is stored in the FIG. 1 test system. 
    
    
     STRUCTURE 
     Referring to FIG. 1, test system 10 includes pattern generator circuit 12, distribution circuit 14 and a plurality of local generator circuits 16. Each local generator circuit provides a signal at node 20 to a circuit under test (CUT) 22. 
     Pattern generator circuit 12 includes conventionally designed high speed pattern generator 30 which provides address patterns at a frequency of 122.0703125 MHz (generally, and hereinafter, referred to as &#34;120 MHz&#34;, and its half as &#34;60 MHz&#34;) and frequency divider circuit 32 which receives the high frequency patterns generated by pattern generator 30 and provides a pair of lower frequency addresses which are half the frequency (i.e., 60 MHz) of the high frequency addresses generated by pattern generator 30. 
     Distribution circuit 14 includes a pair of signal distribution paths 40, 42. Each signal distribution path 40, 42 includes a parallel-multibit bus which simultaneously provides the lower frequency address to d plurality of local generator circuits 16. 
     Each local generator circuit 16 includes a pair of signal generating circuits 50, 52. Signal generating circuit 50 includes local memory 54, which receives information from distribution path 40 and provides a data output to timing generator 56, timing provides a timing generator output to interpolator circuit 58. Likewise, signal path 52 includes local memory 60, which receives information from distribution path 42, timing generator 62, which receives information from local memory 60, and interpolator circuit 64, which receives information from timing generator 62. 
     Interpolator circuits 58 and 64 provide signals to high speed formatter 66. Formatter 66 is a conventional emitter coupled logic (ECL) high speed formatter which receives timing pulses and data and provides a two bit waveform indicating level and tristate at a particular time. Driver 68 receives these signals, and provides an output to node 20 having the correct voltage levels and tristate conditions for the particular CUT. 
     Dual detector 70 is also connected to node 20; dual detector 70 receives signals from node 20 and provides an output to high speed formatter 66. High speed formatter 66 is also connected to a pair of fail processors 72, 74. Fail processors 12, 74 include respective fail memories 76, 78. Each fail memory 76, 78 includes sequence memory portion 80, 82. 
     OPERATION 
     Referring to FIG. 1, system 10 both provides signals to and detects information from node 20 of a CUT. More specifically, when providing signals to node 20, pattern generator 30 generates address patterns at a frequency of 120 MHz. This is provided to frequency divider circuit 32 which receives the 120 MHz address pattern and alternating cycles of half speed (i.e., 60 MHz; address patterns to signal distribution paths 40, 42, respectively. Alternate cycles move respectively over lines 40 and 42, even over the former and odd over the latter; and successive cycles are identified, by their leading edges. Because the pattern is frequency divided prior to transmission to local generators 16, signal distribution paths 40,: 42 need only be appropriate for transmitting signals having a frequency of 60 MHz rather than signals having a frequency of 120 MHz. 
     At power-up and at the start-up of each pattern burst, system 10 is resynchronized. More specifically, frequency divider circuit 32 is configured so that at Dower-up, as well as when it is resynchronized, the next signal provided by frequency divider circuit 32 is over signal path 40. 
     Distribution circuit 14 provides the two half speed address patterns generated by divider circuit 32 to 512 channels. Each channel includes a local generator circuit 16, as shown in FIG. 1. 
     Each local generator circuit 16 provides a high frequency signal to, and detects a high frequency signal from, node 20. When detecting signals from node 20, dual detector receives the high frequency signal and provides the high frequency signal to -formatter 66. Formatter 66 provides two half speed signals to fail processors 72, 74; the half speed signals correspond to the cycles of the half speed address patterns. Fail processors store the failure information in fail memories 76, 78, which function independently at half the speed of formatter 66. Because fail memories 76, 78 function at half the speed of formatter 66, lower cost memories may be used. 
     Information may be stored in fail memories 76, 78 in one of three modes of operation. In a store all (Store All) mode, failure information is continually, alternately written into successive locations of fail memories 76, 78. FIG. 2 shows an example of how the failure information is stored in the Store All mode. In a store this vector (STV) mode, failure information is selectively written into the fail memories based upon the value of a vector bit. In a store only fail (SOF) mode, failure information is written into fail memories 76, 78 on cycles which contain a fail. Or, there may be chosen a combined STV and SOF mode. FIG. 3 shows an example of how the failure information is stored in fail memories 76, 78 for the STV mode and the SOF mode. It is apparent from FIG. 3 that in the STV mode and the SOF mode the failure information is stored in the fail memory which corresponds to the cycle in which the information was generated. Accordingly, to reconstruct the sequence in which the failure information was stored in fail memories 76, 78 further information. is necessary. 
     In order to reconstruct the failure information storage sequence, fail memories 76, 78 use respective sequence memory portions 80, 82. FIG. 4 shows an example of how the failure and sequence information is stored in fail memories 76, 78 and sequence memory portions 80, 82. Sequence memory portions 80, 82 allow the failure information storage sequence to be reconstructed by tracking the failure information as the information is stored. More specifically, a low is stored in a respective sequence memory portion if the previous write was in the same path. A high is stored in a respective sequence memory portion if the previous write was in the other path. By using this information, the failure information storage sequence can be easily reconstructed. 
     OTHER EMBODIMENTS 
     Fail processors 72, 74 may be connected to a common sequence memory. By centrally storing the sequence information, the fail memories may operate independently. Additionally, because the sequence information is centrally stored, fail memories 72, 74 may be distributed without providing local means for determining the sequence of stored bits. 
     Additionally, while the preferred embodiment includes two signal generation paths, the system may operate with one signal generation path but a plurality of fail processors. In such a system, the failure information may be stored at a lower frequency than the generated patterns. 
     Additionally, while the preferred embodiment includes two fail processors and two fail memories, the system may also operate with one fail processor and two fail memories. In such a system, the failure information may be stored at a lower frequency than that at which the fail processor operates. 
     Additionally, while the preferred embodiment shows two fail memories, the number of fail memories may be increased simply by providing more bits to a sequence memory; the bits indicate where in which memory previous write is located.