Abstract: The disclosure described improved apparatus for testing a data processing system including first and second functional members. First and second microprograms for testing the first and second functional members, respectively, are held in a read only store. If an error is detected in the first functional member while the data processing system is processing data, a circuit transmits the starting address of the first microprogram to an address register for the store, so that the first microprogram tests the defective first functional member. As the first functional member is tested, the symptoms needed to diagnose the defect are collected. If the first microprogram is completed without all of the symptoms required for diagnosis being collected, another circuit transmits the first address to the address register so that the first microprogram is executed again. The first microprogram continues to be executed until all of the symptoms needed for diagnosis are collected.

Abstract: A first test and diagnosis device to check a data processing unit. The device includes means for manually testing and passing diagnostics on the first unit, as well as other means for automatically testing and diagnosing the first unit through a second data processing unit. The latter means are comprised of maintenance circuitry, contained within the first unit and linked to the second unit in such a way as to allow the second unit to conversationally interact with the first unit. This interaction is comprised of a sequence of input and output microdialogues performed by means of the maintenance circuits. The test and diagnosis microprograms may be contained in either unit.