Simplified Birthday Statistics and Hamming EDAC

Space systems use error detection and correction (EDAC) schemes to protect memory contents from single event upsets (SEUs). Hamming EDAC is the preferred scheme for fast, random access memories. It allows for the correction of a single bit error within a word and the detection of a double bit error. The common assumption is that the likelihood of an uncorrectable double bit error is very small. This paper develops a simple equation that predicts the cumulative probability of a double bit error occurring within some word of Hamming protected memory as the number of random upsets increase and shows how it can be used to better understand the protection provided by EDAC.