Electronics Terminology: MISR
In electronics, a MISR is a Multi-Input Signature Register, (also called Multi-Input Shift Register).

The MISR is a sequential electronic circuit whose structure is essentially a Linear Feedback Shift Register, (LFSR), which has been modified so that an exclusive or gate drives the input of one or more of the LFSR's flip-flops.

Where are they used?

MISR's are typically used in testing random logic portions of electronic circuits as part of a BIST-based DFT methodology. They are used to compress parallel streams of data from test points within a circuit into a "signature". They are favoured in BIST-based test beacuse of their low probability of "aliasing".

How do they work?

One input of each EXOR gate in the MISR is connected to the LFSR feedback point. The second EXOR input, (the "test data" input), is connected to an output of the logic being tested. The "circuit under test" will usually be stimulated by a LFSR pattern generator clocked at the same rate as the MISR. The "signature" of the test, as read on the MISR's flip-flop outputs', is a function of its regular, LFSR sequence and the inputs from the "logic under test". Unexpected input values from the latter, (caused by a "stuck-at fault", for example), will cause the MISR signature to deviate from the expected value - the circuit fault has been detected at this point. From this point in time forward, the values stored within the MISR will be different to the "fault-free" version, even if no more faults are detected.

At the end of the test sequence, the final signature can be compared to the "expected" final value to determine if a fault has been detected.

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