The document describes the operation of a scan chain used for testing integrated circuits. The scan chain can operate in either shift mode or parallel mode, controlled by the Scan_En pin. In shift mode, each scan cell's input comes from the previous cell's output to shift in a test pattern. In parallel mode, each cell's input comes from the associated combinational logic block. The testing process involves initializing the scan cells, applying a stimulus to primary inputs with Scan_En low, measuring primary outputs, pulsing the clock to capture values, and enabling scan mode to unload the captured values.

1. Scan chain operation

2. PO/SOD
SI
SE
CLK
PI
Scan Pattern operates in one of two modes,
1) Shift Mode.
2) Parallel Mode.
Mode(Active input) is controlled by Scan_En pin.
In Shift mode the input comes from the output of the previous scan
cells or scan input port.
In parallel mode the input to each scan element comes from the
combinational logic block.

3. STEPS:-
●
Initialize scan cells; SE = 1
●
Hold the scan clock off & Apply the stimulus to primary inputs; SE = 0
●
Measure PO; SE = 0.
●
Pulse the clock to capture new value in to scan cell; SE = 0.
●
Enable the scan operation to unload and measure the captured values ;
SE = 1.