scan path

(circuit design) A technique used to increase the

controllability and observability of a logic circuit by

incorporating "scan registers" into the circuit. Normally

these act like flip-flops but they can be switched into a

"test" mode where they all become one long shift register.

This allows data to be clocked serially through all the scan

registers and out of an output pin at the same time as new

data is clocked in from an input pin.

Using this technique, the state of certain points in the

circuit can be examined and modified at any time by suspending

normal operation and switching to test mode. If the scan path

is placed adjacent to the circuit's input and output pins then

this is known as "boundary scan".

(1995-02-14)