| 摘要 |
PURPOSE:To prevent the destruction of data on the external memory when a transient phenomenon like a power failure, etc. occurs, by transmitting the data writing permission signal only when the power supply voltage is higher than a threshold level. CONSTITUTION:When a power supply 6 is steady, an AND circuit 8 is set in an enable state with the same logical value secured between the input and output terminals 1 and 2. When the power supply 6 is set in a transient state, i.e., shows a change L H or H L, an input terminal 8a of an AND circuit 8 has a change L H or H L concurrently with the voltage change of the power supply 6. Here the logical level of the terminal 8a can hold the logical value H only when the voltage of the supply 6 is kept in a satisfactory steady state H owing to the Zener voltage of a Zener diode 3'. Therefore the terminal 8a is set at L in a transient state to prevent the erroneous transmission of signals. |
