| 摘要 |
<p>PURPOSE:To prevent erroneous writing by inhibiting the write of data to a ROM after the end of access based on a specific data signal to be sent out of a microcontroller, control signal and access end signal to be sent out of the ROM. CONSTITUTION:Just after a power source is turned on, the output of a NAND circuit 21 is set to '1' regardless of the value of a write signal WR to be sent out of the microcontroller since a charging voltage is low for a capacitor C1 of a power source turn-on detection circuit, and the write to a ROM 50 is inhib ited. When a power supply voltage VCC is lowered less than a prescribed value during normal operation, the output of a comparator CPM is '1', the output of a NOR circuit 17 is '0', the output of the circuit 21 is '1' and the write to the ROM 50 is inhibited. Thus, when a clock or the power supply voltage is instable, the erroneous write can be prevented.</p> |
