Asynchronous/synchronous interface
The present disclosure includes methods, and circuits, for operating a memory device. One method embodiment for operating a memory device includes controlling data transfer through a memory interface in an asynchronous mode by writing data to the memory device at least partially in response to a write enable signal on a first interface contact, and reading data from the memory device at least partially in response to a read enable signal on a second interface contact. The method further includes controlling data transfer in a synchronous mode by transferring data at least partially in response to a clock signal on the first interface contact, and providing a bidirectional data strobe signal on an interface contact not utilized in the asynchronous mode.
1. A memory interface, comprising:
a bi-directional multiplexed bus for communicating command, address, and data, information; and
control circuitry responsive to at least a first signal on a first signal line, and a second signal on a second signal line, to control the command, address, and data, information on portions of the bus,
wherein the control circuitry utilizes the first signal as a write enable signal in an asynchronous mode and as a clock signal in a synchronous mode, and processes the second signal as a read enable signal in the asynchronous mode and as a write/read signal in the synchronous mode.
2. The memory interface of claim 1 , wherein the control circuitry operates in one of the asynchronous mode or the synchronous mode responsive to a mode selection signal.
3. The memory interface of claim 2 , wherein the mode selection signal is derived from a register bit.
4. The memory interface of claim 2 , wherein the mode selection signal is derived from one of programmable elements selected from the group comprising fuses, metal options, antifuses, and floating gate transistors.
5. The memory interface of claim 2 , wherein the mode selection signal is derived from a clock detection circuit.
6. The memory interface of claim 5 , wherein the control circuitry operates in the synchronous mode responsive to the clock detection circuit detecting a free-running clock signal on the first signal line.
7. The memory interface of claim 1 , wherein the control circuitry operates to perform a write operation in the asynchronous mode responsive to a SET Feature command, thereafter switching to the synchronous mode.
8. The memory interface of claim 1 , wherein the control circuitry operates to perform a write operation in the synchronous mode responsive to a SET feature command, thereafter switching to the asynchronous mode.
9. The memory interface of claim 1 , wherein the control circuitry utilizes a signal on only one additional signal line in the synchronous mode than the quantity of signals that is utilized in the asynchronous mode.
10. The memory interface of claim 9 , wherein the control circuitry utilizes the signal on the one additional signal line as a data strobe signal in the synchronous mode.
11. The memory interface of claim 10 , wherein the data strobe signal is edge-aligned with the data information read from a memory.
12. The memory interface of claim 10 , wherein the data strobe signal is center-aligned with the data information written to a memory.
13. A method of operating a memory interface, comprising:
communicating command, address, and data, information on a bi-directional multiplexed bus;
controlling the command, address, and data, information on portions of the bi-directional multiplexed bus via control circuitry responsive to at least a first signal on a first signal line, and a second signal on a second signal line;
utilizing, by the control circuitry, the first signal as a write enable signal in an asynchronous mode and as a clock signal in a synchronous mode; and
processing, by the control circuitry, the second signal as a read enable signal in the asynchronous mode and as a write/read signal in the synchronous mode.
14. The method of claim 13 , further comprising selecting the synchronous mode at least partially in response to a Set Feature command in the asynchronous mode.
15. The method of claim 13 , further comprising selecting the asynchronous mode at least partially in response to a Set Feature command in the synchronous mode.
16. The method of claim 13 , further comprising switching a data transfer mode from asynchronous to synchronous responsive to presence of a clock signal on the first signal line.
17. The method of claim 13 , further comprising switching a data transfer mode from synchronous to asynchronous responsive to a signal on the first control signal path no longer being a periodic signal corresponding to a predetermined clock frequency and existing for a particular number of cycles.
18. A method of operating a memory interface, comprising:
providing a write enable signal line;
providing a chip enable signal line;
operating the memory interface in an asynchronous mode until a clock signal is present on the write enable signal line; and
operating the memory interface in a synchronous mode while a clock signal is present on the write enable signal line.
19. The method of claim 18 , further comprising operating the memory interface in an asynchronous mode until a chip enable signal is asserted on the chip enable signal line.
20. The memory interface of claim 18 , further comprising:
providing a bidirectional data strobe signal line; and
controlling data transfer responsive to the bidirectional data strobe signal line in the synchronous mode; and
disabling the bidirectional data strobe signal line in the asynchronous mode.