Testing method for efficient testing of micro-controllers

摘要

A micro-controller 12 is operable in three test modes selectable by a register 42 and multiplexer 32 in response to a mode switching signal from a test instrument 28. In an "outer" mode, external instructions from the test instrument are executed in a circuit 30 and the results are sent back to the test instrument. In an "inner" mode, instructions of an in-built self-test program stored in a memory 36 are executed. In the third mode, a ROM read-out device 40 is used for reading the contents of an application program memory 34 so that they can be checked. Provision of the "outer" mode allows up-dating of test procedures.