A methodology for the design of SFS/SCD circuits for a class of unordered codes

We present two design methods that produce concurrently testable and cascadable combinational blocks for a given logic function. In the first method, the designed block is strongly fault-secure and code-disjoint. Any unordered coding scheme can be used for the input and output. The second method produces designs that are strongly fault-secure and strongly code-disjoint. Here the encoding requires some simple density properties that are seen to be satisfied by the commonly used coding schemes. This makes the method applicable to a larger class of coding schemes than the existing methods. We also show that our designs have lower hardware overhead.