MICROCOMPUTER

PURPOSE:To attain freely a function test, etc. of an input and output terminals by supplying a test program, for example, from outside to execute it through a CPU even if no program input terminal is available. CONSTITUTION:The output data Do latched by a buffer I1 is activated by a data output clock phio within the first half cycle of a CPU12 and appears at a data output terminal Po. This terminal Po is cut off from the buffer I1 and ready to accept the input of the external data in the second cycle of the CPU12. Under such conditions, a program Dp supplied to the terminal Po is applied to a latch circuit 20a. The program Dp given from outside can be fed and executed by the CPU12 by an input clock phip within the second half cycle of the CPu12. In other words, the terminal Po can be shared as an input terminal of the program Dp.