JPS6428747A - Microprocessor - Google Patents

Abstract

PURPOSE:To easily check the malfunction of a microprocessor from the external by outputting contents of an arbitrary internal register to the external at the timing when a data input/output terminal is not used. CONSTITUTION:At the time of input, an external resource designated by an address outputs data during the period from the latter half of a cycle S2 to the first half of a cycle S3 out of cycles S0-S3 because a microprocessor 10 takes data inputted from a data input/output terminal 8 into an input data buffer 7 by the last of an instruction. At the time of output, the processor 10 outputs data written in an output data buffer 5 to the external through the data input/output terminal 8 during the period from the latter half of the cycle S1 to the first half of the cycle S3 and outputs a write strobe signal in the period of the cycle S2. Since the data input/output terminal 8 is not used in the period of the cycle S0 in case of input as well as output, contents of a test register 4 are outputted to the terminal 8 in this period. At the time of checking the malfunction by the processor 10, the code of the register whose change of contents should be checked is preliminarily set to a register selecting circuit 3.