Controllable self-checking checkers for conditional concurrent checking

Controllable self-checking (CSC) checkers can be included into concurrent checking schemes where only a subset of code words will be checked for correctness. A CSC checker can have four different working modes, depending on the scheme in which it operates. The checker can work in the system mode as well as in a test mode. In both modes the checker can either perform its usual check function or suppress it, according to a pair of control signals. We present two types of CSC checkers, the OR-type and the XOR-type CSC checker. If a CSC checker does not receive enough code words to be self-checking it can be supported by internal off-line test capability