A term from the world of
electronics.
Boundary Scan is a technique used in the design of integrated circuits to ease the testing
of circuit boards containing multiple ICs.
At the IC level, Boundary Scan is a string of special boundary scan cells implemented as a shift register enclosing all the circuit's core logic. Each element typically has serial in/out and parallel in/out
ports. The idea is to serially shift data along the chain until it
is full; at this point, the data can be exported via the cell's parallel outputs. Data can also be 'captured' via
the cells' parallel inputs and then serially-shifted out for analysis. Operating in this way, the Boundary Scan
logic can be seen as allowing the insertion and sampling of data and points within an IC. The mode of operation
of an IC's Boundary Scan logic is usually controlled by a TAP Controller circuit within the IC.
At the circuit board level, Boundary Scan technique allows access to IC's embedded deep within a circuit board, thus improving
testability and fault diagnosis. Several IC's with Boundary Scan logic can be daisy-chained together to form
one long chain. Under the direction of the TAP Controller, the Boundary Scan logic of certain IC's may be
bypassed to expedite access to any particular IC on a board.
The concept and application of Boundary Scan are described in the following IEEE standard:
IEEE/ANSI 1149.1 standard - 1994