Partial scan and symbolic test at the register-transfer level

This paper presents a partial scan methodology suited for (pipelined) data paths described at the Register-Transfer level. The method is based on feedback elimination by making existing registers scannable or by adding extra transparent scan registers An optimal set (in terms of area cost) of scan registers is selected using an exact branch and bound algorithm. This approach can deal with complex realistic data paths requiring orders of magnitude lower CPU times than gate devel techniques. Furthermore, our symbolic test pattern generation technique can very effectively deal with the delay in the remaining acyclic sequential circuit parts. This symbolic test method makes various scan schemes possible which ensure a correct assembly and application of the test vectors. They are discussed and compared in terms of hardware requirements, test application times and test accuracy.