Abstract:
A method and related apparatus for adjusting/calibrating timing of memory signals. In a preferred embodiment of the invention, reference signals of the same frequency and different phase are generated by a phase-lock loop. These reference signals are used to trigger sampling of signals for generating signals of different timing/delay; then timing/delay of memory signals, such as clock, command, data and data strobe, can be adjusted and calibrated. In this way, the invention can avoid the use of delay lines while adjusting/calibrating memory signals, so as to reduce the negative effects of characteristics shift and variation of delay lines.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The invention relates to a method and related apparatus for adjusting timings of memory signals, and more particularly, to a method and related apparatus of utilizing signals having the same frequency but different phase of a phase locked loop (PLL) to adjust timings of the memory signals. 
   2. Description of the Prior Art 
   Computer systems have become one of the most important hardware foundations in today&#39;s information society. Therefore, improving the efficiency of computer systems has become a major goal. 
   As known by those skilled in the art, a computer system comprises a CPU, a memory (such as DRAM), a chipset, etc. The CPU controls the execution of programs and calculation of data and numbers. The above-mentioned data, programs and numbers can be stored in the memory. The chipset is placed between the CPU and the memory for managing the CPU (or other devices of the computer system) to access the memory. 
   The chipset is electrically connected to the memory through a bus, and controls the data access of the memory through signals of the bus. To control the memory operation timing the chipset has to provide memory clocks to the memory. The chipset has to send command signals in co-ordination with the timing of the memory clocks in order to control the memory to write and/or read data, or to perform other operations such as paging. When the chipset and the memory have to perform a data transmission operation, other signals have to be utilized. For example, when data has to be stored in the memory via the chipset, the chipset not only sends a data signal for transferring data to be stored, but also sends a data indication signal in co-ordination with the timing of the memory clocks to indicate when the memory can receive the data to be stored. 
   In order to complete the access control of the memory correctly, the above-mentioned signals, including the memory clocks, command signals, data signals, and data indication signals, need to have appropriate timing relationships. For example, the data indication signal can align triggering edges (such as rising edges) of the memory clocks, and these triggering edges of the memory clocks and the data indication signals can trigger the memory to receive the command signals and the data signals between set-up time and hold time. 
   In real implementations, however, there are many factors which confuse the above-mentioned normal timing relationship. When the chipset has to transfer the electronic signal to the memory, the memory can be regarded as a circuit load of the chipset. This means that different memory arrangements form different circuit loads and further influence the timing of data transmission. In different memory arrangements, the memory connected to the same bus may comprise only one single-inline memory module (SIMM) or comprise two double-inline memory modules (DIMM). For the chipset, the two-DIMM memory arrangement forms a larger circuit load, therefore, when the signal is transferred into the two-DIMM memory, the signal may be delayed more, meaning that signals generated by the chipset to the memory may not have the correct and appropriate timing relationship. 
   In order to ensure all signals generated by the chipset to the memory do have the correct timing relationship, when the computer system is booting, it performs a timing adjusting operation on all the above-mentioned memory signals generated by the chipset, so as to compensate timing confusion due to non-ideal factors. In the prior art, this timing adjusting operation utilizes different programmable delay lines to inject a corresponding delay time to each memory signal respectively so that memory signals can maintain corresponding timing relationships. For example, if the triggering edge of the data indication signal does not align the triggering edge of the memory clock, the delay line can be utilized to delay the data indication signal so that the delayed data indication signal will properly align the memory clock. 
   There are some disadvantages in utilizing the delay line, however. The parameters of semiconductor procedures vary (e.g. the doping concentration varies), or the temperature of the system varies (according to location, season or specific operation of the system). These factors may cause the injected delay time of each delay line to vary so that the delay line cannot inject a predetermined delay time and consequently the memory signals will not have correct timing relationships. In general, a programmable delay line can utilize a predetermined delay time td as a unit to selectively delay a signal 1*td, 2*td, 3*td etc. But if the delay time varies, the real injected delay time may be 1*(1−5%)td, 2*(1−5%)td etc. For example, when adjusting timing of the memory signals, if the chipset has to delay a signal k*td so that all signals can have correct timing relationships, the chipset programs a corresponding delay line to delay the signal. But if the characteristic of the delay line varies, the delay line may only inject a k*(1−5%)td time delay. There is an error of k*5%*td which may ruin the timing relationships. Furthermore, different delay lines are used for delaying different signals and the time delay error of these different delay lines may be different. This also confuses the timings of the memory signals. Moreover, the delay line may inject other negative influences (such as a jitter phenomenon) to the signals. 
   SUMMARY OF INVENTION 
   The invention provides a method and related apparatus for utilizing reference signals having the same frequency but different phase to adjust timings of memory signals in order to solve the above-mentioned problem. 
   The method for adjusting timing of signals of the present invention comprises: generating a plurality of reference signals, all having the same frequency but different phase; selecting a first reference signal from the reference signals; and adjusting a first signal output delay time according to the first reference signal to make the first signal delay be outputted. 
   Furthermore, the adjusting circuit for adjusting timings of memory signals of a computer system comprises: a clock generator for generating a plurality of reference signals, all having the same frequency but different phase; a multiplexing unit connected to the clock generator for receiving the reference signals, wherein the multiplexing unit selects a first reference signal according to a selecting signal; and an adjusting unit connected to the multiplexing unit for receiving a signal and delaying the output of the signal according to the first reference signal selected by the multiplexing unit. 
   The present invention can utilize the reference signals sampling/triggering technique to adjust timings of memory clocks and command signals. When accurately adjusting the data indication signal and the data signal, the present invention can utilize the above-mentioned reference signals sampling/triggering technique to firstly adjust the timing and secondly utilize delay lines to tune the timing. 
   These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a block diagram of a computer system according to the present invention. 
       FIG. 2  is a timing diagram illustrating memory signals when the computer system shown in  FIG. 1  operates. 
       FIG. 3  is a block diagram illustrating when the chipset shown in  FIG. 1  accomplishes the timing adjusting mechanism according to the present invention. 
       FIG. 4  is a timing diagram of each reference signal shown in  FIG. 3 . 
       FIG. 5  and  FIG. 6  are diagrams illustrating operations of each adjusting unit shown in  FIG. 3 . 
       FIG. 7  is a flow chart illustrating the chipset shown in  FIG. 3  performing the memory signals adjustments. 
       FIG. 8  is a diagram illustrating the related tests shown in  FIG. 7  performing according to the present invention. 
   

   DETAILED DESCRIPTION 
   Please refer to  FIG. 1 , which is a block diagram of a computer system  10 . The computer system  10  comprises a CPU  12 , a chipset  20 , a graphic card  14 , a peripheral device  16  (please note that the number of peripheral devices is not limited and here the one peripheral device  16  is only utilized for an illustration), and two memory slots  22 A and  22 B capable of comprising a memory module and integrating the memory modules respectively placed on the memory slots into the memory of the whole computer system  10 . The chipset  20  is utilized for managing the memory to make the CPU  12  capable of accessing memory data through the chipset. Other devices, for example, the graphic card  14  for processing graphic data and the peripheral device(s)  16  (such as hard disk drive, optical disk drive, network card, and etc.) can exchange data with the CPU  12  and memory through the chipset  20 . 
   For managing and controlling data access of the memory, the chipset  20  can set up one or multiple channels, and is electrically connected to each memory slot through these channels. As shown in  FIG. 1 , the chipset  20  can be electrically connected to the memory slots  22 A and  22 B through the bus of the same channel. Furthermore, the chipset  20  can transfer memory signals including the clock DCLK, the command signal CMD, the data indication signal DQS, and data signal DQ in order to control the operation of memory modules on the memory slots  22 A and  22 B. Here, the clock DCLK is utilized as a memory clock for controlling the timing of the operation of each memory module, the command signal CMD is utilized to send a command to each memory module to control each memory module to perform a needed operation (for example, store data in a specific address of the memory module, read data from the memory module, or perform a paging operation on the memory module), and the data indication signal DQS is utilized to indicate the timing of data transmission. As shown in  FIG. 1 , in order to maintain the accuracy of the clock DCLK, the clock DCLK often firstly passes through a buffer  18  for signal buffering (such as for enhancing the driving ability) and is then transferred to the memory slots  22 A and  22 B. 
   Please refer to  FIG. 2  (in conjunction with  FIG. 1 ).  FIG. 2  is a timing diagram illustrating memory signals when the computer system shown in  FIG. 1  operates. As shown in  FIG. 2 , the horizontal axis represents time. As mentioned above, for accurately controlling data access of the memory, the above-mentioned memory signals must have correct timing relationships. (The correct timing relationship is shown in the left area of  FIG. 2 .) In the correct timing relationship, the triggering edge (in this case, the rising edge) of the clock DCLK (whose period is T) can trigger each memory module to sample the most stable position of the command signal CMD (i.e., the middle of the command signal CMD). That is, it can prevent the memory module from sampling the start, the end, or an unstable position of the command signal CMD. Furthermore, if the correct timing is utilized, the rising edge of the data indication signal DQS can align the rising edge of the clock DCLK. Therefore, in co-ordination with the rising edge and the falling edge of the data indication signal DQS, the data signal DQ can be utilized to transfer data. In  FIG. 2 , we assume that each memory module is a double data rate (DDR) memory module. Therefore, the data signal DQ can transfer one datum per half period. In the correct timing relationship, the operation of coordinating each memory signal can be illustrated as follows. First, at time ta 1 , the memory module installed in the memory slot can be triggered by the clock DCLK to sample the command signal CMD to get the command cmd 1 . Assuming that the command cmd 1  indicates to write data into the memory module, the data indication signal DQS starts a low-level signal (whose period is T from time ta 1 ) as a preamble signal. This represents that the chipset  20  has started to transfer data. At time ta 2 , the chipset  20  operates in co-ordination with the data indication signal DQS and starts to utilize the data signal DQ to transfer data D 1 -D 4  to be written to the memory module. Furthermore, in coordination with the rising edge and falling edge of the data indication signal, the memory module can receive data D 1 -D 4  and store it. 
   But, because of the previously mentioned non-ideal factors, the memory signals will not have correct timing relationships. As mentioned above, different memory arrangements form different loads of the chipset and further influence the timing of the signal transmission. If only one of the memory slots  22 A and  22 B has a SIMM memory module, the load is small and the signal transferred to the memory module is delayed a little. If, however, the memory slots  22 A and  22 B both comprise a DIMM memory module, the two DIMM memory modules form a larger circuit load of the chipset  20 . Therefore, under this memory arrangement, the signal transferred to the memory module may be delayed more and confuse the timing of the memory signals. In the right area of  FIG. 2  is shown a bad timing relationship. Because timings of the command signal CMD and the clock DCLK are confused, when the memory module samples the command signal CMD in the rising edge of the clock DCLK, the memory module may sample an unstable position of the command signal CMD and the correct command cmd 1  cannot be received. Even if the memory module correctly receives the command cmd 1  (assuming that the command cmd 1  is a write-in command), when the memory module starts to receive data from the chipset, the memory module cannot receive the data D 1 -D 4  to be written according to the indication signal DQS because the data indication signal DQS is not aligned well with the clock DCLK. This is because when the memory module receives a write-in command, the memory module must receive the data to be written in a fixed time so that the data can be written correctly. If the memory module receives the data before receiving the write-in command (too early), or a long time after receiving the write-in command (too late), the memory module cannot correctly store the data. 
   In order to prevent this confusion of the timing relationships among the memory signals, the chipset has a related timing adjusting mechanism. This means that the chipset can adjust the timings of the memory signals when the computer system is turned on. Please refer to  FIG. 3  (in conjunction with  FIG. 1 ).  FIG. 3  is a block diagram illustrating when the chipset  20  shown in  FIG. 1  accomplishes the timing adjusting mechanism according to the present invention. The chipset  20  comprises a control module  30 , a clock generator  24 , multiplexer units  36 A- 36 D, adjusting units  38 A- 38 D, setting modules  34 A- 34 D, and  35 C- 35 D, programmable delay lines  40 A- 40 B, a detecting module  28 , a comparing module  26 , and a scanning module  32 . The control module is utilized for controlling the function of the chipset  20  and generating the inner clock DCLKi, the command signal CMCi, the data indication signal DQSi and the data signal DQi of the chipset  20 . The adjusting units  38 A- 38 D are respectively utilized for adjusting the timings of the signals to correspondingly generate the clock DCLK, the command signal CMD, the data indication signal DQS, and the data signal DQ as the memory signals of each memory module. The clock generator  24  can be a PLL, for example, a PLL comprising a ring oscillator for generating N reference signals R_ 1 , R_ 2 , . . . , R_N, all having the same frequency but different phase. Each multiplexer unit  36 A- 36 C can respectively receive a selecting signal Sa-Sb, and Sc 1 -Sc 2  for selecting a reference signal from the N reference signals according to the selecting signal. The clock generator  24 , the multiplexer units  36 A- 36 D, the delay lines  40 A- 40 B, the adjusting units  38 A- 38 D, the control module  30 , the setting module  34 A- 34 D, and  35 C- 35 D, the detecting module  28 , the comparing module  26 , and the scanning module can be combined to accomplish a computer system memory signal timing adjusting circuit to achieve the purpose of adjusting the memory signal timings. 
   According to the selected reference signals Ra and Rb selected by the multiplexer units  36 A- 36 B, the adjusting units  38 A- 38 B can respectively adjust the timings of the clock DCLKi and the command signal CMDi. Furthermore, for tuning timings of the data indication signal DQSi and the data signal DQi, the reference signals Rc 0  and Rd 0  selected by the multiplexer units  36 C and  36 D can first pass through the programmable delay lines  40 A and  40 B to delay their timings so that delayed reference signals Rc and Rd are generated. Therefore, the adjusting units  38 C and  38 D can adjust the timings of the data indication signal DQSi and data signal DQi according to the reference signals Rc and Rd. The delay lines  40 A and  40 B can be controlled by the selecting signals Sc 2  and Sd 2  to set delay times. Each set of selecting signals, Sa-Sb, Sc 1 -Sd 1 , Sc 2 -Sd 2 , is generated by the selecting modules  34 A- 34 D,  35 C- 35 D. These setting modules can be registers, which can control corresponding multiplexer units or delay lines through corresponding selecting signals according to the data stored in the registers. Furthermore, the data to be stored in the setting module can be determined by the control module  30 , detecting module  28 , and scanning module  32 . 
   In order to further illustrate the operation of timing adjustment of the chipset  20 , please refer to  FIG. 4  (in conjunction with  FIG. 3 ).  FIG. 4  is a timing diagram of each reference signal shown in  FIG. 3 .  FIG. 4  shows N reference signals R_ 1 , R_ 2 , . . . , R_N generated by the clock generator  24 . In  FIG. 4 , the horizontal axis is time. The period of the reference signals is T (T is the period of the memory clock), but the phases of the reference signals are averagely distributed in 360 degrees, and the phase difference can be regarded as the delay time. For example, corresponding to the rising edge of the first reference signal R_ 1 , the rising edge of the n th  reference signal R_n has a (n−1)*T/N delay time. As shown in  FIG. 4 , in the preferred embodiment, the clock generator  24  can generate 8 reference signals (that is, N=8). 
     FIG. 5  and  FIG. 6  are diagrams illustrating the operations of each adjusting unit shown in  FIG. 3 . Please refer to  FIG. 5  (in conjunction with  FIG. 3  and  FIG. 4 ).  FIG. 5  illustrates the operation of the adjusting unit  38 B. The adjusting unit  38 B can comprise one or multiple flip-flops, which can be triggered by the reference signal R_i to sample an input signal Si to obtain a corresponding output signal So. As shown in  FIG. 5 , if the input signal Si has three data Si 0 -Si 2  (where the period of each is T) at time tb 0 , and the reference signal R_i is the reference signal R_ 3 , the adjusting unit  38 B orderly starts to sample according to the rising edges of the reference signal R_ 3  in order to obtain a corresponding output signal So. This makes the output signal So start to transfer data Si 0 -Si 2  after time tb 1 . In other words, when the adjusting unit  38 B is triggered by the reference signal R_ 3 , the output signal So is equivalent to delaying the input signal Si from time tb 0  to time tb 1 . Similarly, for the same input signal Si, if the adjusting unit  38 B receives the reference signal R_instead of the above-mentioned reference signal R_ 3 , the output signal is equivalent to delaying the input signal Si from time tb 0  to time tb 2 . The time difference between time tb 1  and time tb 2  corresponds to the phase difference between the reference signal R_ 3  and the reference signal R_ 7 . Therefore, selecting different reference signals to trigger the adjusting unit  38 B is equivalent to delaying the input signal Si a certain time. The present invention utilizes the above-mentioned method to adjust the timings of the memory signals. 
   Please refer to  FIG. 6  (in conjunction with  FIGS.3 ,  4 ).  FIG. 6  shows the operation of the adjusting unit  38 D. The adjusting unit  38 D also receives a reference signal R_i to sample the input signal Si according to the reference signal R_i in order to adjust the timing of the input signal so that the output signal So is formed. As shown in  FIG. 6 , when the adjusting unit  38 D operates, the input signal Si can comprise two signals Si_H and Si_Furthermore, the two signals Si_H and Si_L have a half period T between the two signals, and respectively carry data (for example, the signal Si_H carries data D 1  and D 3 , and signal Si_L carries data D 2  and D 4 ), whose period is T. Therefore, the two signals Si_H and Si_L can both form an input signal Si, whose period is T/ 2 . When the adjusting unit  38 D is triggered by the reference signal R_i, the adjusting unit  38 D samples the signal Si_H in the rising edge of the reference signal R_i, samples the signal Si_L in the falling edge of the reference signal R_i (or in the rising edge of another reference signal having a 180 degrees phase difference between the reference signal R_i), and generates the output signal So according to the sampling results. 
   For example, when the reference signal R_i is the reference signal R_ 3  shown in  FIG. 4 , the rising edge of the reference signal R_ 3  triggers the adjusting unit  38 D at time tc 1  to start sampling the data D 1  of the signal Si_H. Then the falling edge of the reference signal R_ 3  triggers the adjusting unit  38 D to sample the data D 2  of the signal Si_L. In addition, the adjusting unit  38 D assembles the sampled data into the corresponding output signal So. As shown in  FIG. 6 , when the adjusting unit  38 D is triggered by the reference signal R_ 3 , the output signal So is equivalent to the result of delaying the input signal Si from time tc 0  to time tc 1 . Similarly, if the adjusting unit  38 D is triggered by the reference signal R_ 7 , the output signal So is equivalent to the result of delaying the input signal Si from time tc 0  to time tc 2 . In other words, even if the input signal Si carries data/information whose period is T/ 2 , the present invention can still utilize the reference signals to adjust the timings. 
   Similar to the adjusting units  38 B and  38 D shown in  FIGS.5 ,  6 , the adjusting units  38 A and  38 C can utilize similar methods to adjust the timings of the clock DCLKi and the data indication signal DQSi according to each reference signal and then generate the clock DCLK and the data indication signal DQS. Please refer to  FIG. 7  (in conjunction with  FIGS.1 ,  3 ).  FIG. 7  is a flow chart of the flow  100  illustrating the chipset  20  shown in  FIG. 3  performing memory signal adjustments. The flow  100  comprises the following steps: 
   Step  102 : Start. The flow  100  can be performed when the computer system  10  (shown in  FIG. 1 ) adjusts the corresponding timings of the memory signals. 
   Step  104 : Utilize the clock generator  24  (here the clock generator can be a PLL) to generate a plurality of reference signals R_ 1 , R_ 2 , . . . , R_N, all having the same frequency but different phases. 
   Step  106 : Select an appropriate reference signal to adjust the timings of the clock DCLKi and the command signal CMDi to make the corresponding output clock DCLK and the corresponding command signal CMD have a correct timing relationship. When the computer system  10  is booting, the memory arrangement is detected to see if the same bus (channel) comprises memory modules, what type of memory module is placed, etc. Then, according to the memory arrangement, the equivalent circuit load, caused by the memory arrangement to the chipset, is determined, and the influences on timings of the memory signals are also determined. When the step  106  is performed, the detecting module  28  (shown in  FIG. 3 ) of the chipset  20  can evaluate which reference signal is utilized according to the detecting result of the memory arrangement, and correspondingly set the setting modules  34 A and  34 B to control corresponding multiplexer units  36 A and  36 B in order to select an appropriate reference signal. Therefore, the adjusting units  38 A and  38 B can adjust the timings of the clock DCLKi and the command signal CMDi to compensate for the timing influences of the memory arrangement according to the reference signals. In the real implementation, the chipset provider can first test the influences of different memory arrangements and evaluate which corresponding reference signal has to be utilized. Therefore, the detecting module  28  can directly check a look-up table, which is established by the above-mentioned chipset provider, to select a correct reference clock according to the actual memory arrangement. This helps the adjusting module  28  to adjust the timings of the clock DCLK and the command signal CMD. 
   Step  108 : After adjusting the timings of the clock DCLK and the command signal CMD, the two signals can be utilized as a reference to adjust the timings of the data indication signal DQSi and the data signal DQi. This makes the outputted data indication signal DQS/data signal DQ and the clock DCLK/command signal CMD have a good timing relationship. When performing step  108 , the scanning module  32  first utilizes the setting modules  35 C and  35 D to fix the delay time of each delay line  40 A and  40 B, and controls the multiplexer units  36 C and  36 D to select the same reference signal to adjust the timings of the data indication signal DQSi and the data signal DQi. Then the control module  30  can send a command (through the clock DCLK and the command signal CMD) to the memory, write specific data into the memory in coordination with data indication signal DQS/data signal DQ, and read the written data from the memory. The comparing module  26  can compare the read data with the data to be written. If the read data does not comply with the data to be written, this represents that the timings of the data indication signal DQS/data signal DQ can not co-ordinate correctly with the timings of the clock DCLK/command signal CMD so the data is incorrectly written. At this time, the scanning module  32  can utilize another reference signal to adjust the timings of the data indication signal DQS/data signal DQ again, and write the data into the memory again to test if the reference signal works. If the read data complies with the data to be written, this represents that the reference signal works. In other words, the reference signal can make the timings of the data indication signal DQS/data signal DQ co-ordinate with the timings of the clock DCLK/command signal CMD. As mentioned above, after the clock DCLK/command signal CMD triggers the memory module to receive a write-in command, the data to be written have to be transferred into the memory module in a fixed time. An early transmission or a late transmission may cause a failure. Therefore, according to the above-mentioned read/written tests, we can determine whether the timings of the data indication signal DQS/data signal DQ can co-ordinate with the timings of the other memory signals. In addition, when performing step  108 , the scanning module  32  can orderly select all N reference signals. In other words, the scanning module  32  can test according to all reference signals, that is, the scanning module  32  can utilize all reference signals to see if the adjusted data indication signal DQS/data signal DQ makes the data write/read smoothly. Please refer to  FIG. 8 , which is a diagram illustrating the scanning module  32  orderly performing (N−1) th , N th , (N+1) th  write/read tests according to the present invention. The scanning module  32  orderly performs these tests, but because of comparison of these tests, the timings of related signals of all the tests are shown in parallel in  FIG. 8 . When orderly performing these tests, the scanning module  32  respectively utilizes the reference signals R_(n−1), R_n, and R_(n+1) to adjust the timings of the data indication signal DQS/data signal DQ, and controls the memory module to receive the data D 1 -D 4  in coordination with the command cmd of the command signal CMD. As shown in  FIG. 8 , through different reference signals, the timings of the data indication signal DQS/data signal DQ are delayed increasingly. The timing difference of the data indication signal DQS/data signal DQ between two tests is equal to N/T. 
   After the above-mentioned tests, the scanning module  32  can select a better reference signal according to the test results, and set the setting modules  34 C and  34 D according to the better reference signal so that the multiplexer modules  36 C and  36 D can fixedly utilize the better reference signal in the following operation. 
   Step  110 : Utilize the delay lines  40 A and  40 B to tune the timings of the data indication signal DQS/data signal DQ. In the embodiment of  FIG. 3 , the present invention utilizes the delay lines  40 A and  40 B to respectively delay the reference signal selected by the multiplexer units  36 C and  36 D. Furthermore, the delay time injected by the delay lines  40 A and  40 B influences the data indication signal DQS/data signal DQ through the adjusting units  38 C and  38 D. Similar to step  108 , the scanning module  32  can orderly select different parameters to set the programmable delay lines  40 A and  40 B so that the delay lines  40 A and  40 B can orderly provide different delay times. In addition, the scanning module  32  can perform a test of writing/reading data according to each delay time, and tune the timings of the data indication signal DQS/data signal DQ according to the test results. In other words, the scanning module  32  can select a better delay time and utilize this better delay time to set the setting modules  35 C and  35 D. This makes all the memory signals (including the clock DCLK, the command signal CMD, the data indication signal DQS, and the data signal DQ) have better (fine-tuned) timing relationships. 
   Step  112 : Finish the operation of adjusting timings and complete the boot procedure of the computer system  10 . Then, the chipset  20  can utilize the better parameters set by the setting modules to control the multiplexer units, the delay lines to select a better reference signal and the delay times to adjust timings of the memory signals. This ensures the memory signals have better(proper) timing relationships in the following operation of the computer system. 
   To sum up, the present invention utilizes a plurality of reference signals, all having the same frequency but different phase to adjust the memory signals. In contrast to the prior art of utilizing the delay lines, the present invention not only can efficiently prevent the delay time shift (errors) of the delay lines, but can also reduce the jitter phenomenon injected by the delay line. Although the present invention also utilizes the delay lines, the present invention reduces the delay time injected by the delay lines. Actually, the delay time injected by the delay lines can be less than T/N (where T is the period of the clock DCLK and N is the number of the reference signals). In the present invention, because the delay time difference caused by the phase difference of the reference signals is T/N, if the delay time is larger than T/N, another reference signal can be selected to compensate the delay time, so that the delay time can be limited to be less than T/N. In other words, because the present invention is based on the timing adjustment of the reference signals, the timing adjustment does not depend on the delay lines as much as the prior art. Furthermore, the present invention can be widely utilized in the timing adjustment of other serial control circuits. Please note that the modules and adjusting units shown in  FIG. 3  can be accomplished through hardware or firmware; for example, the functions of the control module, the comparing module, the detecting module, and the scanning module can be accomplished through the same controller, and the adjusting units can be accomplished through a logic circuit of hardware. 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.