| 摘要 |
<p>PURPOSE:To protect a memory by providing a holding means to hold the data read propriety information showing the read-out propriety of the data supplied from outside and stored in a RAM and controlling the propriety of reading the data out of the RAM based on the data read-out propriety information. CONSTITUTION:If it is required to inhibit the read of data in order to protect the data stored in a RAM 2, the protection ON information is supplied to the data input of a delayed flip-flop FF 5 from an external host device. If a command signal received from the host device under such conditions, the FF 5 fetches the protection ON information in response to the timing of the command signal. The protection ON information is defined as a signal of a low level and therefore the Q output of the FF 5 is changed into a low level thereafter. Thus an AND gate 4 is closed. Therefore the read signal R received from a memory control circuit 3 is prevented by the gate 4 and never supplied to the RAM 2. As a result, a memory can be protected.</p> |
