Scan chain

Scan chain

Scan chains are a technique used in Design For Test. The objective is to make testing easier by providing a simple way to set and observe every flip-flop in an IC. A special signal called "scan enable" is added to a design. When this signal is asserted, every flip-flop in the design is connected into a long shift register, one input pin provides the data to this chain, and one output pin is connected to the output of the chain. Then using the chip's clock signal, an arbitrary pattern can be entered into the chain of flips flops, and/or the state of every flip flop can be read out.

In a full scan design, Automatic test pattern generation is particularly simple. No sequential pattern generation is required - combinatorial tests, which are much easier to generate, will suffice. If you have a combinatorial test, it can be easily applied.
*Assert scan mode, and set up the desired inputs.
*De-assert scan mode, and apply one clock. Now the results of the test are captured in the target flip-flops.
*Re-assert scan mode, and see if the combinatorial test passed.There are many variants:
*Partial scan: Only some of the flip-flops are connected into chains.
*Multiple scan chains: Two or more scan chains are built in parallel, to reduce the time to load and observe.
*Test compression: the input to the scan chain is provided by on-board logic

See also

*Design For Test
*Automatic test pattern generation
*Electronic design automation
*Integrated circuit design
*Serial Peripheral Interface Bus


Wikimedia Foundation. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • Scan Test — bezeichnet bei (modernen) digitalen Schaltungen ein spezielles Verfahren zum Testen auf strukturelle (das heißt fertigungsbedingte) Schäden. Es beruht auf einer Hintereinanderschaltung sämtlicher im Entwurf verwendeter Flip Flops mit einer Modus… …   Deutsch Wikipedia

  • Scan-based trading — (SBT) or Scan based trading is the process where suppliers maintain ownership of inventory within retailers warehouses or stores until items are scanned at the point of sale. HistoryTraditionally Scan Based Trading programs use Electronic Data… …   Wikipedia

  • Scan — may refer to: *Scan, the act of examining sequentially, part by part *Image scanning, in data processing, the act of optically analyzing a two or three dimensional image and digitally encode it (digitize it) for storage in a computer file *Scan,… …   Wikipedia

  • Chain Reaction (label) — Chain Reaction Filiale de Basic Channel Fondé en 1995 Fondateur Basic Channel Genre(s) Dub Techno …   Wikipédia en Français

  • Boundary scan — is a method for testing interconnects (wire lines) on printed circuit boards or sub blocks inside an integrated circuit.The Joint Test Action Group (JTAG) developed a specification for boundary scan testing that was standardized in 1990 as the… …   Wikipedia

  • Optical scan voting system — Election technology Certification of voting machines Independent Testing Authority (ITA) NVLAP VVSG End to end auditable voting systems Help America Vote Act Independent verific …   Wikipedia

  • Boundary scan description language — (BSDL) is a description language for electronics testing using JTAG. It has been added 1996 to the IEEE Std. 1149. Boundary Scan Description Language (BSDL) is a subset of VHDL that is used to describe how JTAG (IEEE 1149.1) is implemented in a… …   Wikipedia

  • Joint Test Action Group — (JTAG) is the usual name used for the IEEE 1149.1 standard entitled Standard Test Access Port and Boundary Scan Architecture for test access ports used for testing printed circuit boards using boundary scan.JTAG was an industry group formed in… …   Wikipedia

  • Design for testing — Design for Test (aka Design for Testability or DFT ) is a name for design techniques that add certain testability features to a microelectronic hardware product design. The premise of the added features is that they make it easier to develop and… …   Wikipedia

  • Design For Test — (aka Design for Testability or DFT ) is a name for design techniques that add certain testability features to a microelectronic hardware product design. The premise of the added features is that they make it easier to develop and apply… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”