Scan structure for CMOS storage elements
AssigneeHewlett-Packard Development Company, L.P.
InventorSamuel D. Naffziger
Life of this patent
Estimating the term…
Abstract
Scan chain links which step data through a scan chain using only a single control signal, and which require a reduced number of transistors to scan data into and out of a latch. One scan chain link, which allows the output of a scanned latch to “wiggle”, uses eight transistors and only a single control signal. Another scan chain link, which prevents the output of a scanned latch from “wiggling”, and which allows data to be maintained in a latch during a scan operation if it is so desired, uses twenty-five transistors and two control signals: one control signal for stepping data through a scan chain, and an additional control signal for preventing the output of a scanned latch from wiggling.
Claims22
A scan chain which services a plurality of storage elements, said scan chain comprising:
- a) a control line over which a single signal is propagated, said single signal enabling data propagation through the scan chain;
- and
- b) a plurality of scan chain links, at least some comprising:
- i) a first tri-statable element coupled to said control line, said first tri-statable element comprising an input for receiving a scan output of an upstream storage element which is being serviced by the scan chain, and an output for providing data to a storage element which is being serviced by the scan chain link;
- and
- ii) a second tri-statable element coupled to said control line, said second tri-statable element comprising an input for receiving data from the storage element which is being serviced by the scan chain link, and an output which provides a scan output to a downstream storage element which is being serviced by the scan chain.
A scan chain which services a plurality of storage elements, said scan chain comprising:
- a) a control line over which a single signal is propagated, said single signal enabling data propagation through the scan chain;
- and
- b) a plurality of scan chain links, at least some comprising:
- i) a scan storage element for periodically receiving data stored in a storage element which is being serviced by the scan chain link;
- ii) a first tri-statable element coupled to said control line, said first tri-statable element comprising an input for receiving a scan output of an upstream storage element which is being serviced by the scan chain, and an output for providing data to the scan storage element;
- and
- iii) a second tri-statable element coupled to said control line, said second tri-statable element comprising an input for receiving data from the scan storage element, and an output which provides a scan output to a downstream storage element which is being serviced by the scan chain.
In a scan chain which services a plurality of storage elements, a scan chain link, comprising:
- a) storage means for periodically receiving and storing a copy of data which is held in a storage element N which is being serviced by the scan chain, said storage means receiving said copy of data held in the storage element N in response to assertion of a signal which loads data into the storage element N;
- b) a first tri-statable element comprising an input for receiving a scan output of a storage element N−1 which is being serviced by the scan chain, an output coupled to a first node of said storage means, and a number of control inputs;
- c) a second tri-statable element comprising an input coupled to a second node of said storage means, an output which provides a scan output for the storage element, and a number of control inputs;
- and
- d) means for loading the storage element N with data stored in the storage means.
A method of scanning data out of a number of storage elements, comprising, alternately:
- a) closing a first tri-statable element while opening a second tri-statable element, the first tri-statable element being coupled to a storage element N, said closing advancing data stored in the storage element N to a scan output node;
- and
- b) closing the second tri-statable element while opening the first tri-statable element, the second tri-statable element being coupled to a storage element N+1, said closing storing data appearing on the scan output node in the storage element N+1.
Dependencies are inferred from the claim text.