Semiconductor memory having burst transfer function
View Patent ↗A refresh control circuit generates a refresh request in a predetermined cycle. A first burst control circuit outputs a predetermined number of strobe signals in accordance with an access command. A burst access operation is executed by an access command. A data input/output circuit successively inputs data to be transferred to a memory cell array or successively outputs data supplied from the memory cell array, in synchronization with the strobe signals. An arbiter determines which of a refresh operation or a burst access operation is to be executed first, when the refresh request and the access command conflict with each other. Therefore, the refresh operation and burst access operation can be sequentially executed without being overlapped. As a result, read data can be outputted at a high speed, and write data can be inputted at a high speed. That is, the data transfer rate can be improved.
1. A semiconductor memory comprising:
a memory cell array having memory cells;
a first burst control circuit for outputting a strobe signal having a predetermined number of pulses, the output corresponding to an access command for successively burst accessing said memory cell array; and
a data input/output circuit for successively inputting/outputting data to be transferred to/from said memory cell array in synchronization with each of said pulses of the strobe signal, wherein
said first burst control circuit comprises:
a level detecting circuit for detecting that one of command signals supplied as said access command turns to its active level; and
an output control circuit for starting outputting said strobe signal after measuring a predetermined time from the detection of said level detecting circuit.
2. The semiconductor memory according to claim 1 , wherein
during a read operation, said first burst control circuit starts outputting said strobe signals said predetermined time after detection of an active level of a chip enable signal that is one of said command signals, said strobe signal being a signal for outputting data transferred from said memory cell array.
3. The semiconductor memory according to claim 1 , wherein
during a read operation, said first burst control circuit starts outputting said strobe signals said predetermined time after detection of an active level of an output enable signal that is one of said command signals, said strobe signal being a signal for outputting data transferred from said memory cell array.
4. The semiconductor memory according to claim 1 , wherein
during a write operation, said first burst control circuit starts outputting said strobe signals said predetermined time after a detection of an active level of a chip enable signal that is one of said command signals, said strobe signal being a signal for inputting data to be transferred to said memory cell array.
5. The semiconductor memory according to claim 1 , wherein
during a write operation, said first burst control circuit starts outputting said strobe signals said predetermined time after a detection of an active level of a write enable signal that is one of said command signals, said strobe signal being a signal for inputting data to be transferred to said memory cell array.
6. The semiconductor memory according to claim 1 , wherein
said predetermined time in read operation and in write operation are different from each other.
7. The semiconductor memory according to claim 1 , wherein
said predetermined time in read operation and in write operation are equal to each other.
8. The semiconductor memory according to claim 1 , further comprising
an address counter for receiving an external address supplied corresponding to said access command and for sequentially generating internal addresses that follow said external address, wherein
said address counter counts up to generate said internal addresses, in response to start of outputting said strobe signal.
9. The semiconductor memory according to claim 1 , further comprising
a mode register for setting said predetermined time from exterior, and wherein
said first burst control circuit measures said predetermined time in accordance with a value set in said mode register.
10. The semiconductor memory according to claim 1 , further comprising
a switch structured by a conductive pattern which is formed on the semiconductor substrate in accordance with a pattern shape of a photomask used in a fabrication process of the semiconductor memory, and wherein
said first burst control circuit measures said predetermined time in accordance with a voltage value of a destination of said conductive pattern.
11. The semiconductor memory according to claim 1 , further comprising
a fuse in which information indicative of said predetermined time is programmed, and wherein
said first burst control circuit measures said predetermined time in accordance with the information programmed in said fuse.