Accelerated scan circuitry and method for reducing scan test data volume and execution time
An architecture and methodology for test data compression using combinational functions to provide serial coupling between consecutive segments of a scan-chain are described. Compressed serial-scan sequences are derived starting from scan state identifying desired Care_In values and using symbolic computations iteratively in order to determine the necessary previous scan-chain state until computed previous scan-chain state matches given known starting scan-chain state. A novel design for a new flip-flop is also presented that allows implementing scan-chains that can be easily started and stopped without requiring an additional control signal. Extensions of the architecture and methodology are discussed to handle unknown (X) values in scan-chains, proper clocking of compressed data into multiple scan-chains, the use of a data-spreading network and the use of a pseudo-random signal generator to feed the segmented scan-chains in order to implement Built In Self Test (BIST).
1. An integrated circuit (IC), comprising:
a multiplicity of mode-control signals, each adapted to assume one of at least two states;
a multiplicity of scan-chains, each comprising at least one flip-flop;
a multiplicity of blocking circuits, each of said blocking circuits receiving at least one data-in signal and adapted to be responsive to at least one mode-control signal, each of said multiplicity of blocking circuits providing serial scan data to at least one flip-flop of said multiplicity of scan-chains;
wherein each of said blocking circuits outputs a value that is representative of a combination of a value on said at least one data-in signal of said blocking circuit and at least one value of at least one scan bit position previous to said at least one flip-flop, in at least a first state of said multiplicity of mode control inputs; and
each of said blocking circuits outputs a constant value, in at least a second state of said multiplicity of mode control inputs.
2. The integrated circuit according to claim 1 , further comprising:
a multiplicity of multi-input signature register (MISR) blocks that are adapted to be responsive to a multiplicity of outputs of said multiplicity of blocking circuits.
3. The integrated circuit according to claim 1 , wherein each of said blocking circuits comprises:
a multiplexer adapted to be responsive to at least one said mode-control signal;
a logic gate adapted to be coupled to a first data input of said multiplexer, said logic gate adapted to receive as inputs at least one data-in signal and at least one additional input from a scan bit position previous to said at least one flip-flop.
4. The integrated circuit according to claim 3 , wherein said at least one additional input from a scan position previous to said at least one flip-flop is coupled to at least a second data input of said multiplexer; and
wherein said multiplexer is adapted to produce an output value that is representative of a signal value at said first data input in a first state of said mode-control signal; and
wherein said multiplexer is adapted to produce an output value that is representative of signal value at said at least a second data input in a second mode of said mode-control signal.
5. The integrated circuit according to claim 1 , further comprising:
a multiplicity of multi-input signature register (MISR) blocks, wherein each of said MISR blocks is prevented from capturing “X” states from a multiplicity of tap points on said scan chain when one or more of said tap points contains said “X” state.
6. The integrated circuit according to claim 1 , wherein at least one of said blocking circuits is adapted to eliminate “X” states within a scan chain by selectively replacing at least one value of at least one scan bit position previous to at least one flip-flip with said constant value when at least one “X” state is propagated from said at least one scan bit position previous to said at least one flip-flop of said scan chain to said at least one flip-flop of said scan chain through said at least one of said blocking circuits.