Internal signal monitoring circuit

1. An apparatus comprising:

a first circuit configured to measure a first time period from a first active edge of one of plurality of internal signals to a second active edge of another one of the plurality of internal signals; and

a second circuit configured to compare the first time period with a second time period to generate an alert signal.

2. The apparatus of claim 1 , further comprising a third circuit configured to store an alert signal,

wherein the alert signal is output to outside in response to a first command issued from outside.

3. The apparatus of claim 2 ,

wherein the third circuit includes a mode register circuit, and

wherein the first command is a mode register read command.

4. The apparatus of claim 1 ,

wherein the first active edge is an edge of a first internal signal among the plurality of internal signals, and

wherein the second active edge is an edge of a second internal signal different from the first internal signal among the plurality of internal signals.

5. The apparatus of claim 4 , wherein the second circuit is configured to activate the alert signal when the first time period is longer than the second time period.

6. The apparatus of claim 5 , wherein the first and second internal signals are generated in response to a second command issued from outside.

7. The apparatus of claim 6 ,

wherein the second command is an active command, and

wherein the first and second internal signals are ones of row-system signals sequentially generated based on the active command.

8. The apparatus of claim 4 , wherein the second circuit is configured to activate the alert signal when the first time period is shorter than the second time period.

9. The apparatus of claim 8 , wherein the first and second internal signals are generated in response to second and third commands, respectively, issued from outside.

10. The apparatus of claim 9 ,

wherein the second command is an active command,

wherein the third command is a read command or a write command,

wherein the first internal signal is one of row-system signals generated based on the active command, and

wherein the second internal signal is one of column-system signals generated based on the read command or the write command.

11. The apparatus of claim 1 , wherein the first circuit is configured to start a counting operation in response to the first active edge and stop the counting operation in response to the second active edge to generate a first binary data indicating the first time period.

12. The apparatus of claim 11 , wherein the second circuit is configured to compare the first binary data with a second binary data indicating the second time period.

13. The apparatus of claim 12 , further comprising a fourth circuit configured to non-volatilely store the second binary data.

14. The apparatus of claim 1 , wherein the first and second circuits are activated during an initial sequence performed at a power on.

15. An apparatus comprising:

a memory cell array including a plurality of memory cells;

an access control circuit configured to perform an access operation to the memory cell array using first and second signals sequentially activated;

a signal monitor circuit configured to evaluate a time period from when the first signal is activated to when the second signal is activated and generate an alert signal when the time period is an aberrant value;

a mode register circuit configured to store the alert signal; and

an I/O circuit coupled to the memory cell array and the mode register circuit,

wherein the access control circuit is configured to perform, in response to a data read command, a read operation to the memory cell array so that a-read data stored in one of the memory cells is output to outside through the I/O circuit and perform, in response to a mode register read command, a mode register read operation to the mode register circuit so that the alert signal is output to outside through the I/O circuit.

16. The apparatus of claim 15 , wherein the signal monitor circuit is activated during an initial sequence performed at a power on.