| 摘要 |
<p>PURPOSE:To enhance the protective effect against undesired rewriting caused by a runaway, etc., of a main control part, etc., by providing a supply power source switching circuit for supplying selectively a program voltage to a flash memory (EEPROM), and a switch means which can control the supply to a switching circuit of a signal. CONSTITUTION:A supply power source switching circuit 5 switches a supply voltage to a program terminal VPP/VCC of a memory 2 under the control of a switch means 1.3. That is, an input of a logic voltage VCC is connected to the VPP/VCC terminal through a countercurrent preventive diode 6. On the other hand, an input of a program voltage VPP is connected to the VPP/ VCC terminal through a first switching transistor TR 17 of PNP type. Also, a base of the TR 17 is connected to the input of the program voltage VPP through a first resistance 8, and also, grounded through a second resistance 9 and a second switching transistor TR 210 of NPN type. In such a way, even when a CPU, etc., run away, rewriting of an EEPPOM is not generated as far as the switch means 1.3 inhibits the supply of a signal.</p> |
