Apparatus and method prohibiting RAM diagnosis when other units may access RAM

Abstract

Erroneous diagnosis caused by a case where hardware other than an ALU (arithmetical and logic unit) has a function to access a RAM directly due to the construction of a CPU is to be prevented. In order to do so, interrupt is prohibited at every predetermined diagnosis timing. Then, determination is made as to whether a start-up of a DMAC (direct memory access controller) is approved or not, and only when the start-up is not approved, the diagnosis is performed to a diagnosis object RAM by previously determined diagnosis unit bytes at a time through a read/write method. When failure of the RAM is determined, the diagnosis procedure is advanced to an NG process. When the start-up of the DMAC is approved, the diagnosis of the diagnosis object RAM is prohibited, and the address of the object RAM is stored in a memory so that the object RAM is diagnosed at a next diagnosis timing.

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