Scan chain
Beginner
A long line of the chip’s memory cells linked together in test mode. Values go in one end and come out the other, like a bucket brigade.
Novice
Scan flip-flops wired output-to-input into one long shift register, from a scan-in pin to a scan-out pin. Each clock tick moves every bit one place along. Chips use many chains side by side to save time.
Expert
Shift time per pattern is set by the longest chain, so chains are balanced in length. Chains are usually grouped by clock domain and clock edge, with lockup latches where they must cross. Chain order is reworked after placement to shorten wires.
Explained in Design for test (Design Flow).
See also: Scan flip-flop, Lockup latch, Scan-chain reordering.