Data storing method of dynamic RAM and semiconductor memory device
View Patent ↗When a DRAM enters an operation mode in which only a data storing operation is performed, a check bit for error detection and correction for plural data is generated and stored. Refresh operation is performed in a refresh cycle which is made long within an allowable range of an error occurrence by an error correcting operation using the check bit. Before the DRAM returns to the normal operation mode from the data holding operation mode, an error bit is corrected by using the data and the check bit.
1. A method of operating a DRAM having a normal operation mode for data reading and writing, and a data retention mode, comprising:
generating and storing a check bit for error detection and correction when the DRAM enters the data retention mode;
performing a refresh operation in the data retention mode in which a refresh cycle is extended within an allowable error correction range; and
correcting an error bit using stored data and the check bit before the DRAM returns to the normal operation mode from the data retention mode,
wherein in at least one refresh cycle of the refresh operation, memory cells of the DRAM are refreshed but error detection and correction are not preformed.
2. The method according to claim 1 , wherein the check bit for error detection and correction is generated and stored using an error detection and correction circuit.
3. The method according to claim 2 , wherein the error detection and correction circuit does not operate in all refresh cycles of the data retention mode.
4. The method according to claim 2 , wherein before the DRAM enters the data retention mode the error detection and correction circuit is made active to enable parity bit calculation.
5. The method according to claim 2 , wherein before the DRAN returns to the normal operation mode, the DRAM enters a data correcting mode in which the error detection and correction circuit is made active to execute calculation of corrected data and error position and correcting and writing of corrected data.
6. The method according to claim 1 , wherein the length of the refresh cycle is changed by a memory cell leak monitor.
7. The method according to claim 1 , wherein the length of the refresh cycle is adjusted in accordance with ambient temperature.