Buffered memory device

1. A memory module comprising:

a DRAM device configured to generate a low DQS state on a DQS line; and

a buffer coupled to the DRAM device, the buffer having a plurality of drivers, wherein the buffer is configured to detect the low DQS state by comparing the low DQS state to a low voltage level of one of the plurality of drivers, wherein the low voltage level is adjustable, and wherein the buffer is configured to execute a training routine to adjust the low voltage level.

2. The memory module of claim 1 , wherein the buffer comprises a comparator configured to compare the low DQS state to the low voltage level.

3. The memory module of claim 1 , wherein the buffer is configured to enter a READ mode in response to detecting the low DQS state.

4. The memory module of claim 3 , wherein the buffer is configured to stay in the READ mode until the DRAM device tri-states its connection to the DQS line.

5. The memory module of claim 1 , comprising a register coupled to the DRAM device, the register configured to buffer command and address information for the DRAM device.

6. A memory module comprising:

a memory device; and

a buffer communicatively coupled between the memory device and a memory controller, the buffer configured to switch between a WRITE mode and a READ mode based on a state of a data strobe, wherein the buffer comprises:

a data module coupled to a data pin of the memory device; and

a DQS module configured to control a data transmission direction of the data module, wherein the data module comprises:

a first driver configured to drive signals onto the memory device; and

a second driver configured to drive signals to the memory controller; and

wherein the DQS module comprises a comparator with an output that is coupled to control inputs of the first and second differential drivers.

7. The memory module of claim 6 , wherein the buffer comprises a comparator configured to determine the state of the data strobe.

8. The memory module of claim 6 , wherein the comparator is coupled to a DQS line and configured to generate the output based on a state of the DQS line.

9. The memory module of claim 8 , wherein the comparator is configured to turn on the second driver if the comparator determines that the memory device is driving a low DQS state onto the DQS line.

10. The memory device of claim 9 , wherein the comparator is configured to turn off the first differential driver if the comparator determines that the memory device is driving a low DQS state onto the DQS line.

11. The memory module of claim 6 , wherein the comparator is configured to differentiate between a low DQS state driven by the memory device and a low DQS state driven by a third driver in the DQS module.

12. The memory module of claim 11 , wherein the memory device is configured to drive a DQS low state at a first voltage level, wherein the first voltage level is not equal to a second voltage level of the low DQS state driven by the third driver.

13. The memory module of claim 12 , comprising logic configured to control the second voltage level.

14. The memory module of claim 13 , wherein the logic is configured to set a voltage level that is recognized by the memory device as a low DQS state.

15. The memory module of claim 6 , wherein the DQS module comprises:

a first dual output differential driver configured to drive DQS signals onto the memory device; and

a second dual output differential driver configured to drive DQS signals to the memory controller, wherein the first and second dual output differential drivers are coupled to the comparator.

16. A method comprising:

detecting a low DQS state being driven on a DQS line by a memory device; and

switching to a READ mode in response to the detection, wherein switching to the READ mode comprises turning off a first differential driver and turning on a second differential driver.

17. The method of claim 16 , comprising:

detecting a tri-state from the memory device on the DQS line; and

switching from the READ mode a WRITE mode in response to the tri-state detecting.

18. A memory system comprising:

a memory controller; and

a memory module comprising:

a plurality of memory devices; and

a buffer coupled between the plurality of memory devices and the memory controller, the buffer configured to switch between a WRITE mode and a READ mode based on a state of a DQS line between the memory controller and the memory module, wherein the memory devices are configured to generate a DQS low state having a voltage level unequal to a low voltage level of a driver coupled to the DQS line, wherein the driver is within the buffer.