MICRO CONTROLLER HAVING A SMALL NUMBER OF TEST PINS, ESPECIALLY USING OTHER USAGE EXCEPT THE TEST AS A TEST PIN

摘要

PURPOSE: A micro controller having a small number of test pins is provided to perform a test using a pin used for other usage except the test. CONSTITUTION: According to the micro controller having a reset pin inputting an inverted reset signal and the first and the second pins(10,12) connected to a crystal oscillator, a comparison unit(16) compares a level of the inverted reset signal with a fixed value. An amplification unit(18) amplifies an oscillation signal inputted to the first pin from the crystal oscillator and then outputs it as a clock signal of the micro controller. A signal transmission unit(20) outputs the clock signal to the crystal oscillator through the second pin in response to the comparison result. And an AND gate unit(22) performs an AND operation of the comparison result and a supply power inputted in a test mode through the second pin, and outputs the AND operation signal as a test signal of the micro controller.