Hierarchical scan selection

  • US 4,872,169 A
  • Filed: 12/08/1988
  • Issued: 10/03/1989
  • Est. Priority Date: 03/06/1987
  • Status: Expired due to Term
First Claim
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1. A boundary scan test system comprising:

  • a plurality of logic devices, each having input and output lines for selectively transmitting and receiving data;

    a first and second of said logic devices, each further including a logic core and a scan cell having multiple bit positions;

    said scan cells being logically located between said logic core and said input and output lines of said first and second logic devices wherein selected bits of said multiple bit positions, under control, are selectively substituted for said data;

    each of said first and second said logic devices further including a device select module connected to respective said scan cells of said first and second said logic devices;

    said device select module of said first logic device being also coupled to a first bus for receiving test data bits and being further coupled to said device select module of said second logic device via a second bus;

    said device select module of said first logic device, in response to selected ones of said test data bits, selectively loading other selected ones of said test data bits into said scan cell connected to said device select module of said first logic device and transmitting other selected ones of said test data bits to said device select module of said second logic device via said second bus; and

    said device select modules further controlling the said substitution of data by said connected scan cells.

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