Memory device and method of controlling the same
In a single data rate (SDR) mode, logic level transitions of a data condition prior-determination signal RDYO are outputted to an output terminal (O) in response to an internal clock signal CKI. A ready signal RDY is outputted in synchronization with the internal clock signal CKI following a logic level transition of the data condition prior-determination signal RDYO. In a double data rate (DDR) mode, on the other hand, a toggle signal is outputted to the output terminal (O) in correspondence with the internal clock signal CKI following a logical level transition of the data condition prior-determination signal RDYO. After the internal clock signal CKI following the logical level transition of the data condition prior-determination signal RDYO, a strobe signal DQS is outputted in synchronization with the internal clock signal CKI. The ready signal RDY is outputted at the data condition informing terminal (X) in SDR mode while, on the other hand, the strobe signal DQS is outputted at the data condition informing terminal (X) in DDR mode.
1. A memory device which is operable in a first operation mode for setting one edge of an external clock signal as a data determining edge and a second operation mode for setting both edges of the external clock signal as the data determining edge, the memory device comprising:
a data condition informing terminal which provides a condition of data to be outputted; and
a data condition signal control section which generates a first signal indicating a logical level transitioning at a first time preceding an initial data determining edge at a start of data output in the first operation mode and a second signal indicating a logical level is toggled every first time preceding each data determining edge on and after the start of data output in the second operation mode, and wherein the data condition signal control section outputs the first or second signal to the data condition informing terminal.
2. The memory device according to claim 1 , wherein the first time is a time between a data determining edge in which the first or second signal is determined and a preceding data determining edge thereto.
3. The memory device according to claim 2 , wherein the first time is a time synchronized with the preceding data determining edge.
4. The memory device according to claim 1 , wherein a data transition time at which data transits in logic level prior to the data determining edge in the second operation mode is a time synchronized with transition of the second signal.
5. The memory device according to claim 4 , wherein a time to output initial data among the data transition times is a time different from a time at which the second signal is toggled.
6. The memory device according to claim 1 , wherein the first signal is a data valid flag to inform that data to be outputted is valid and the second signal is a strobe signal representing the data to be outputted.
7. The memory device according to claim 1 , wherein the data condition signal control section comprises:
a shift resistor section which transmits a signal indicating a condition of a first node to the data condition informing terminal at the first time;
a first control section which sets the first node to the logical level generated as the first signal at a second time preceding the first time in the first operation mode; and
a second control section which sets the first node to an inversion signal of a signal from the data condition informing terminal at a second time preceding the first time in the second operation mode.
8. The memory device according to claim 7 , wherein the second time is a time between a preceding data determining edge prior to the first time and an earlier preceding data determining edge earlier than the preceding data determining edge.
9. The memory device according to claim 8 , wherein the second time is a time synchronized with the earlier preceding data determining edge.
10. The memory device according to claim 7 further comprising an internal clock generator generating an internal clock signal synchronized with the data determining edge,
wherein the first and second times are times synchronized with the internal clock signal.
11. The memory device according to claim 7 , wherein the first control section including a first switch portion having a first terminal to be connected to the first node and a second terminal in which a signal of the logical level to be generated as the first signal is inputted.
12. The memory device according to claim 11 , wherein
the first switch section is activated in the first operation mode, and
the signal of the logical level is inputted to the second terminal of the first switch section by a time corresponding to the second time after the preceding data determining edge prior to the second time.
13. The memory device according to claim 11 , wherein the first switch section is activated by a time corresponding to the second time after the preceding data determining edge prior to the second time.
14. The memory device according to claim 7 , wherein the second control section comprises:
a second switch section having a first terminal to be connected to the first node;
a logical inverting section having an input terminal connected to the data condition informing terminal and an output terminal connected to a second terminal of the second switch section.
15. The memory device according to claim 14 , wherein the second switch section is activated by a time corresponding to the second time after the preceding data determining edge prior to the second time.
16. The memory device according to claim 14 , wherein
the second control section further comprises a third switch section having a first terminal connected to the first node and a second terminal connected to the data condition informing terminal, and wherein
the second control section is activated until a time corresponding to the preceding data determining edge prior to the second time in the second operation mode.
17. A control method in a memory device which is operable in a first operation mode for setting one edge of an external clock signal as a data determining edge and a second operation mode for setting both edges of the external clock signal as the data determining edge, the control method comprising the steps of:
generating a first signal having a logical level which transits at a first time preceding an initial data determining edge at the start of data output in the first operation mode;
generating a second signal having a logical level which is toggled every first time preceding each data determining edge on and after the start of data output in the second operation mode; and
outputting one of the first and second signals from a data condition informing terminal by selecting one of the first signal generating step and the second signal generating step.
18. The control method in a memory device according to claim 17 , wherein the first time is a time between the data determining edge in which the first or second signal is determined and the preceding data determining edge.
19. The control method in a memory device according to claim 18 , wherein the first time is a time synchronized with the preceding data determining edge.
20. The control method in a memory device according to claim 17 , wherein the first signal is a data valid flag to inform that data to be outputted is valid and the second signal is a strobe signal representing the data to be outputted.
21. The control method in a memory device according to claim 17 , wherein the first and second signal generating steps and the outputting step include:
a step of transmitting a signal at the first time to the data condition informing terminal:
a step of setting the signal to be transmitted at a logical level to be outputted as the first signal at a second time preceding the first time in the first operation mode; and
a step of setting the signal to be transmitted as an inversion signal of a signal from the data condition informing terminal at a second time preceding the first time in the second operation mode.
22. The control method in a memory device according to claim 21 , wherein the second time is a time between the preceding data determining edge prior to the first time and an earlier preceding data determining edge earlier than the preceding data determining edge.
23. The control method in a memory device according to claim 22 , wherein the second time is a time synchronized with the earlier preceding data determining edge.
24. The control method in a memory device according to claim 21 further comprising an internal clock signal synchronized with the data determining edge,
wherein the first and second times are times synchronized with the internal clock signal.