| 摘要 |
PURPOSE:To hold surely and simply a CRT screen even at power supply interruption by changing over the mode to a self-refresh mode when a dynamic RAM is not in the operation of a normal access mode. CONSTITUTION:A high level signal via a line l18 is impressed to a data terminal D at power supply ON, a Q output of a D FF7B goes to a high level, a terminal RFSH of a dynamic RAM9 for CRT display goes to a high level and the RAM9 is selected to the normal access mode. On the other hand, when the power supply is interrupted and the terminal D is inverted to a low level, a horizontal synchronizing signal via a line l11 and an inverter 7A by the backup of a battery or the like is impressed, the FF7B is latched in synchronizing with the blanking period of the horizontal synchronizing signal, the output Q is inverted to a low level, and the RAM9 is brought into the self-refresh mode during a period not in the normal access mode operating period. As a result, even if the power supply interruption is generated at any timing, the holding of the CRT screen is performed simply and surely. |
