Patent ID: 11927633
Assignee: TEXAS INSTRUMENTS INCORPORATED
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 8:
9. A method implemented by a device under test comprising a scan chain including a plurality of storage elements and an output buffer, the method comprising:
receiving, in a scan in phase, a scan clock signal and a scan in signal to load the storage elements of the scan chain;
loading, in the scan in phase, a shadow shift register of the device under test from a scan output of one of the storage elements of the scan chain, wherein the loading is responsive to the scan clock signal;
receiving, in a capture phase, a signature clock signal and a signature data signal to load a signature register of the device under test, wherein a value of the shadow shift register is latched before the capture phase;
comparing, in a scan out phase, the latched value of the shadow shift register and a value of the signature register;
unloading, in the scan out phase, the storage elements of the scan chain through the output buffer responsive to the scan clock signal and responsive to the latched value of the shadow shift register being equal to the value of the signature register; and
providing, in the scan out phase, a high-impedance output by the output buffer responsive to the latched value of the shadow shift register being unequal to the value of the signature register.