| 摘要 |
PURPOSE:To prevent a program from being decoded by the third person, by destructing the test circuit for check of contents of the progarm ROM of the microcomputer locally or overall from the external of the computer to make the test circuit into an unusable state. CONSTITUTION:Between the ground power source and the fixed power source of voltage Vcc of the microcomputer having program ROM 1 and test circuit 2, a series circuit where resistance 3, diode 4 and resistance 5 are connected from the voltage Vcc side is provided. Terminal 2a for test mode selection of test circuit 2 is connected to the connection point of resistance 3 and diode 4, and test terminal 7 which accepts signals and is connected to the chip of the microcomputer is connected to the connection point of diode 4 and resistance 5 through fuse 6. After completion of product test, voltage V3 which satisfies condition VB<V3<VD for breakdown voltage VD of diode 4 and fusing voltage VB of fuse 6 is applied to terminal 7, and fuse 6 is fused to make circuit 2 into the unusable state. |
