Appeal No. 1998-2767 Application 08/391,541 card systems. Typically, a processor simply writes a pattern of data to a particular memory location and then reads back the data from that location to verify proper operation. This process is then repeated for different patterns and different memory locations. The invention provides a diagnostic state machine distinct from the central processor unit. To isolate a fault between a computer system and an external device connected to the computer via an external bus, the computer system simulates a direct memory access (DMA) by the external device without actually employing the external device. To accomplish this, the computer system stores self-generated data and address signals from a back connector that would otherwise connect to the external device. The method of the invention is performed by writing a first value to a first address space defined by addresses on a bus, latching the first value in a first register with a diagnostic state machine, writing the first value from the first register to a second address within the second address space defined by addresses on the bus, reading a second value from the memory over the bus, at the second address, and comparing the second 2Page: Previous 1 2 3 4 5 6 7 8 9 10 NextLast modified: November 3, 2007