Full Serial Integrated Scan
Download
Report
Transcript Full Serial Integrated Scan
TOPIC : Scan based Design
Module 4.3 : Scan architectures and testing
UNIT 4 : Design for Testability
Introduction
There are several forms of scan designs;
they differ primarily in how the scan cells
are designed.
We will illustrate three generic forms of
scan design :
◦ Full Serial Integrated Scan
◦ Isolated Serial Scan
◦ Non-serial Scan
Normal sequential circuit
Full serial integrated scan circuit
Full Serial Integrated Scan Architecture
Full Serial Integrated Scan
The normal parallel-load register R has
been replaced by a scan register Rs.
When N_bar/T = 0 (normal mode), Rs
operates in the parallel-latch mode; hence
both circuits operate the same way.
Now Y becomes easily controllable and E
easily observable. Hence test generation
cost can be drastically reduced.
Isolated Serial Scan
In this, scan register is in the normal data
path.
This scan architecture, the selection of
the CPs and Ops associated with the scan
register Rs is left up to the desigener.
Full isolated scan
If Rs is used both to
observe and control all
the storage cells in S.
A test vector yl is
scanned (shifted) into Rs,
loaded into R', and then
applied to the circuit C.
The response e can be
loaded into R',
transferred to Rs, and
then scanned out.
The register Rs is said to
act as a shadow
register to R'.
Non serial Scan
It aim to give full controllability and
observability to all storage cells in a circuit.
Storage cells are arranged in a randomaccess bit – addressable memory.
During normal operation the storage cells
operate in their parallel-load mode.
Scan in – appropriate cell is addressed, the
data are applied to Sin. The output of the
cells are wired-OR together.
Advantage – Only bits in R that need to
changes must be addressed and modified;
this saves scanning data through entire
register.
Non serial Scan Example
Random-access scan