Memory having test circuit

1. A memory circuit comprising:

a memory; and

a first test circuit coupled to the memory, the first test circuit configured to:

compare data read from memory cells with expected data for the memory cells to provide a first set of pass/fail signals for the memory cells;

compress the first set of pass/fail signals for the memory cells into a second pass/fail signal;

latch the second pass/fail signal in response to a data valid signal;

maintain the latch of the second pass/fail signal if the second pass/fail signal indicates a failed test;

combine the second pass/fail signal and a third pass/fail signal of a second test circuit to provide a fourth pass/fail signal; and

pass the fourth pass/fail signal to a third test circuit.

2. The memory of claim 1 , wherein the first test circuit is configured to compare data read from four memory cells with expected data for the four memory cells to provide a first set of four pass/fail signals for the four memory cells.

3. The memory of claim 1 , wherein the second test circuit is configured the same as the first test circuit, and wherein the third test circuit is configured the same as the first test circuit.

4. The memory of claim 1 , wherein the memory comprises a dynamic random access memory.

5. The memory of claim 1 , wherein the memory comprises a synchronous dynamic random access memory.

6. The memory of claim 1 , wherein the memory comprises a double data rate synchrounous dynamic random access memory.

7. The memory of claim 1 , wherein the memory comprises a double data rate two synchrounous dynamic random access memory.

8. A memory comprising:

a first array of memory cells;

a plurality of compare circuits configured to compare data read from a portion of the first array of memory cells with expected data for the portion of the first array of memory cells to provide a first set of pass/fail signals for the portion of the first array of memory cells;

a first compression circuit configured to compress the first set of pass/fail signals into a second pass/fail signal;

a latch configured to latch the second pass/fail signal in response to a data valid signal; and

a merge circuit configured to merge the second pass/fail signal with a third pass/fail signal to provide a fourth pass/fail signal indicating the pass/fail status for the first array of memory cells.

9. The memory of claim 8 , wherein the latch comprises a flip-flop latch configured to latch the second pass/fail signal in response to a rising edge of the data valid signal.

10. The memory of claim 8 , wherein the latch is configured to maintain the latch of the second pass/fail signal in response to subsequent data valid signals if the second pass/fail signal indicates a failed test.

11. The memory of claim 8 , wherein the plurality of compare circuits comprises four compare circuits configured to compare data read from four memory cells with expected data for the four memory cells to provide a first set of four pass/fail signals for the four memory cells.

12. The memory of claim 8 , further comprising:

a second compression circuit configured to receive the fourth pass/fail signal and a fifth pass/fail signal from a second array of memory cells and provide a global pass/fail signal for first array of memory cells and the second array of memory cells.

13. The memory of claim 12 , further comprising:

a tri-state buffer configured to pass the global pass/fail signal to a data pad in response to an enable signal.

14. A memory comprising:

means for writing expected data to a portion of an array of memory cells;

means for reading data from the portion of the array of memory cells;

means for comparing the data read from the portion of the array of memory cells to the expected data to provide a set of first pass/fail signals for the portion of the array of memory cells, each memory cell in the portion of the array of memory cells having one first pass/fail signal;

means for merging the set of first pass/fail signals for the portion of the array of memory cells to provide a second pass/fail signal; and

means for latching the second pass/fail signal in response to a data valid signal.

15. The memory of claim 14 , further comprising:

means for maintaining the latch of the second pass/fail signal in response to subsequent data valid signals if the second pass/fail signal indicates a failed test.

16. The memory of claim 14 , further comprising:

means for combining the latched second pass/fail signal with a third pass/fail signal for another portion of the array of memory cells to provide a global pass/fail signal.

17. The memory of claim 16 , further comprising:

means for passing the global pass/fail signal to a data pad.

18. A method for testing a memory, the method comprising:

comparing data read from a first set of memory cells of a first memory bank with expected data for the first set of memory cells to provide a first set of pass/fail signals for the first set of memory cells;

compressing the first set of pass/fail signals for the first set of memory cells into a second pass/fail signal;

latching the second pass/fail signal in response to a data valid signal; and

maintaining the latch of the second pass/fail signal in response to subsequent data valid signals if the second pass/fail signal indicates a failed test.

19. The method of claim 18 , further comprising:

comparing data read from a second set of memory cells of the first memory bank with expected data for the second set of memory cells to provide a second set of pass/fail signals for the second set of memory cells;

compressing the second set of pass/fail signals for the second set of memory cells into a third pass/fail signal;

latching the third pass/fail signal in response to the data valid signal; and

maintaining the latch of the third pass/fail signal in response to subsequent data valid signals if the third pass/fail signal indicates a failed test.

20. The method of claim 19 , further comprising:

combining the second pass/fail signal and the third pass/fail signal to provide a fourth pass/fail signal for the first memory bank.

21. The method of claim 20 , further comprising:

comparing data read from a third set of memory cells of a second memory bank with expected data for the third set of memory cells to provide a third set of pass/fail signals for the third set of memory cells;

compressing the third set of pass/fail signals for the third set of memory cells into a fifth pass/fail signal;

latching the fifth pass/fail signal in response to the data valid signal; and

maintaining the latch of the fifth pass/fail signal in response to subsequent data valid signals if the fifth pass/fail signal indicates a failed test.

22. The method of claim 21 , further comprising:

comparing data read from a fourth set of memory cells of the second memory bank with expected data for the fourth set of memory cells to provide a fourth set of pass/fail signals for the fourth set of memory cells;

compressing the fourth set of pass/fail signals for the fourth set of memory cells into a sixth pass/fail signal;

latching the sixth pass/fail signal in response to the data valid signal; and

maintaining the latch of the sixth pass/fail signal in response to subsequent data valid signals if the sixth pass/fail signal indicates a failed test.

23. The method of claim 22 , further comprising:

combining the fifth pass/fail signal and the sixth pass/fail signal to provide a seventh pass/fail signal for the second memory bank.

24. The method of claim 23 , further comprising:

combining the fourth pass/fail signal and the seventh pass/fail signal to provide a global pass/fail signal for the first memory bank and the second memory bank.

25. A method for testing a memory, the method comprising:

simultaneously writing expected data to memory cells of a plurality of memory banks of a memory;

simultaneously reading data from the memory cells of the plurality of memory banks of the memory;

simultaneously comparing the data read from the memory cells to the expected data to provide a test result for each memory bank;

latching the test result for each memory bank in response to a data valid signal for each memory bank; and

combining the test result for each memory bank into a global test result for the memory.