Abstract: A method and system for testing a memory in operation. A storage unit is used to temporarily free one memory location in the memory, making it possible to check this memory location for bit errors. Data intended for the selected memory location is stored in the storage unit, and instead a test pattern is written into the memory location to be tested and read out again, all in coordination with the normal operation of the memory. If the pattern read from the test location does not match the written test pattern, an alarm is raised.

Abstract: A self-diagnostic asynchronous data buffer includes an addressable buffer having a write address determined by a write counter and a read address determined by a read counter. A write clock controls storage into the buffer and updating of the write counter. A read clock controls reading from the buffer and updating of the read counter. The self-diagnostic asynchronous data buffer additionally has a test register, an address counter, and a state machine. To determine whether a hardware fault exists, the state machine compares the address counter output with the output of the write counter. When the two are equal, the next write to the addressable buffer causes the input data to also be stored in the test register. Next, the address counter output is compared with the output of the read counter. When the two addresses are equal, the output data from the addressable buffer is compared to the value stored in the test register. Inequality between these two values indicates a hardware fault.