Feedback Scan Isolation and Scan Bypass Architecture
First Claim
1. A scan isolation and bypass architecture comprising core logic having a core logic input and a core logic output;
- an input isolation multiplexer having a first input, a second input, a selection input and an output, the input isolation multiplexer selectively providing one of the first and second inputs of the input isolation multiplexer to the output of the input isolation multiplexer based on the selection input of the input isolation multiplexer, the first input of the input isolation multiplexer being coupled to a functional input, the second input of the input isolation multiplexer being coupled to a functional output, the output of the input isolation multiplexer being coupled to the core logic input, and the selection input of the input isolation multiplexer being coupled to a first test select signal;
an output isolation multiplexer having a first input, a second input, a selection input and an output, the output isolation multiplexer selectively providing one of the first and second inputs of the output isolation multiplexer to the output of the output isolation multiplexer based on the selection input of the output isolation multiplexer, the first input of the output isolation multiplexer being coupled to the core logic output, the second input of the output isolation multiplexer being coupled to the output of the input isolation multiplexer, the output of the output isolation multiplexer providing the functional output, and the selection input of the output isolation multiplexer being coupled to a second test select signal;
wherein when the first and second test select signals indicate a core feedback test, the output isolation multiplexer passes the core logic output from the first input of the output isolation multiplexer to the output of the output isolation multiplexer as the functional output, and the input isolation multiplexer passes the core logic output from the second input of the input isolation multiplexer to the output of the input isolation multiplexer and the core logic input.
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Abstract
A feedback scan isolation and bypass architecture apparatus and method. The apparatus includes core logic, and input and output multiplexers. The input multiplexer selectively provides a functional input or the core output to the core input based on a test signal. The output multiplexer selectively provides the core output or the input multiplexer output to a functional output based on the test signal. When the test signal indicates core feedback testing, the output multiplexer outputs the core output and the input multiplexer feeds back the core output to the core input. When the test signal indicates bypass testing, the input multiplexer outputs the functional input and the output multiplexer outputs the functional input bypassing the core logic. Logic can block the feedback or bypass signals when there are timing issues. Logic can modify the number of feedback or bypass signals when the number of functional inputs and outputs are different.
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Citations
25 Claims
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1. A scan isolation and bypass architecture comprising core logic having a core logic input and a core logic output;
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an input isolation multiplexer having a first input, a second input, a selection input and an output, the input isolation multiplexer selectively providing one of the first and second inputs of the input isolation multiplexer to the output of the input isolation multiplexer based on the selection input of the input isolation multiplexer, the first input of the input isolation multiplexer being coupled to a functional input, the second input of the input isolation multiplexer being coupled to a functional output, the output of the input isolation multiplexer being coupled to the core logic input, and the selection input of the input isolation multiplexer being coupled to a first test select signal; an output isolation multiplexer having a first input, a second input, a selection input and an output, the output isolation multiplexer selectively providing one of the first and second inputs of the output isolation multiplexer to the output of the output isolation multiplexer based on the selection input of the output isolation multiplexer, the first input of the output isolation multiplexer being coupled to the core logic output, the second input of the output isolation multiplexer being coupled to the output of the input isolation multiplexer, the output of the output isolation multiplexer providing the functional output, and the selection input of the output isolation multiplexer being coupled to a second test select signal; wherein when the first and second test select signals indicate a core feedback test, the output isolation multiplexer passes the core logic output from the first input of the output isolation multiplexer to the output of the output isolation multiplexer as the functional output, and the input isolation multiplexer passes the core logic output from the second input of the input isolation multiplexer to the output of the input isolation multiplexer and the core logic input. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A scan isolation and bypass architecture comprising
core logic means for processing a core logic input to generate a core logic output; -
an input selection means for passing one of a first input and a second input to an output based on a selection input, the first input of the input selection means being coupled to a functional input, the second input of the input selection means being coupled to a functional output, the output of the input selection means being coupled to the core logic input, and the selection input of the input selection means being coupled to a first test select signal; an output selection means for passing one of a first input and a second input to an output based on a selection input, the first input of the output selection means being coupled to the core logic output, the second input of the output selection means being coupled to the output of the input selection means, the output of the output selection means providing the functional output, and the selection input of the output selection means being coupled to a second test select signal; wherein when the first and second test select signals indicate a core feedback test, the output selection means passes the core logic output to the output of the output selection means as the functional output and the input selection means passes the core logic output to the output of the input selection means as the core logic input. - View Dependent Claims (13, 14)
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15. A method of scan isolation and bypass testing for a core coupled to external logic, the core having core inputs and core outputs, the external logic providing functional inputs to the core inputs and accepting functional outputs from the core outputs, the method comprising:
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causing the functional inputs from the external logic to bypass the core and pass to the functional outputs when a test selection signal indicates bypass testing; causing the core outputs to feedback to the core inputs when the test selection signal indicates core logic feedback testing; and causing the functional inputs to be processed by the core and the core outputs to pass to the external logic as the functional outputs when the test selection signal indicates normal processing. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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Specification