Counter circuit, latency counter, semiconductor memory device including the same, and data processing system
To provide a counter circuit capable of accurately counting a high-frequency signal in which hazard or the like is easily generated. There are provided: a frequency dividing circuit that generates first and second frequency dividing clocks, which differ in phase to each other, based on a clock signal; a first counter that counts the first frequency dividing clock; a second counter that synchronizes with the second frequency dividing clock to fetch a count value of the first counter; and a selection circuit that exclusively selects count values of the first and second counters. According to the present invention, a relation of the count values between the first and second counters is kept always constant, and thus, even when hazard occurs, the count values are only made to jump and the count values do not fluctuate.
1. A method comprising:
producing a first clock signal;
producing second and third clock signals in response to the first clock signal, the second and third clock signals being substantially equal in frequency to each other and differing in phase from each other;
updating a count value in response to the second clock signal to produce an updated count value; and
fetching the updated count value in response to the third clock signal to produce a fetched count value.
2. The method as claimed in claim 1 , wherein the producing the second and third clock signals comprises:
frequency-dividing the first clock signal to produce a frequency-divided clock signal; and
performing logical operations on the first clock signal and the frequency-divided clock signal.
3. The method as claimed in claim 1 , wherein each of the second and third clock signals changes between first and second logic levels, and the method further comprises selecting and outputting the updated count value when the second clock signal takes one of the first and second logic levels and the fetched count value when the third clock signal takes the one of the first and second logic levels.
4. The method as claimed in claim 3 , further comprising counting a latency of a data read command in response to the updated count value and the fetched count value.
5. The method as claimed in claim 1 , further comprising:
reading data from a memory cell array in response to an access command to produce read-out data;
producing an internal command signal in response to the access command; and
outputting the read-out data in response to the internal command signal, the first clock signal, the updated count value and the fetched count value.
6. The method as claimed in claim 4 , the producing the first clock signal is carried out by use of a DLL circuit.
7. A method comprising:
generating a system clock signal;
producing a first clock signal in response to the system clock signal;
producing second and third clock signals in response to the first clock signal, the second and third clock signals being substantially equal in frequency to each other and differing in phase from each other;
updating a count value in response to the second clock signal to produce an updated count value;
fetching the updated count value in response to the third clock signal to produce a fetched count value;
outputting data in response to the updated count value and the fetched count value; and
receiving the data.
8. The method as claimed in claim 7 , wherein the generating the system clock signal and the receiving the data are executed by a memory controller; and the producing the first clock signal, the producing the second and third clock signals, the updating the count value, the fetching the updated count value, and the outputting the data are executed by a memory that is coupled to and controlled by the memory controller.
9. The method as claimed in claim 7 , wherein the first clock signal is produced by a DLL technology.
10. The method as claimed in claim 7 , wherein the producing the second and third clock signals comprises:
frequency-dividing the first clock signal to produce a frequency-divided clock signal; and
performing logical operations on the first clock signal and the frequency-divided clock signal.
11. The method as claimed in claim 7 , further comprising:
issuing a data read command;
accessing to a memory cell array in response to the data read command to produce read-out data; and
producing an internal command signal in response to the data read command;
and
wherein the outputting the data comprises outputting the read-out data in response to the internal command signal, the first clock signal; the updated count value and the fetched count value.
12. The method as claimed in claim 11 , wherein the generating the system clock signal, the issuing the data read command and the receiving the data are executed by a memory controller; and the producing the first clock signal, the producing the second and third clock signals, the updating the count value, the fetching the updated count value, the accessing the memory cell array, the producing the internal command signal and the outputting the data are executed by a memory device that is coupled to and controlled by the memory controller.
13. The method as claimed in claim 11 , wherein the outputting the data comprises counting a latency of the internal command signal in response to the updated count value and the fetched count value.
14. The method as claimed in claim 1 , wherein each of the updated count value and the fetched count value is represented by binary data comprising a plurality of bits.
15. The method as claimed in claim 1 , wherein the updating the count value is performed by a ripple counter and the fetching the update count value is performed by a set of flip-flop circuits.