A method for automatically updating the frequency of an internal RC oscillator

Abstract

The invention discloses a method for automatically updating the frequency of an internal RC oscillator. The calculation principle of the invention is combined with a binary approximation method, and the median of the minimum and maximum values ​​of available correction numbers is taken. After comparison and calculation, the median required for the next step is obtained, and an iterative calculation is performed to obtain a correction setting value closer to the target frequency, and finally an optimal frequency correction setting value within an error range is derived. When the available correction number is large, the invention has the effects of short calculation time, small number of calculations, and improved accuracy. At the same time, it has the characteristics of few required pins, intuitive and easy calculation, and simple test model setting.

Description

Technical Field

[0001] The invention relates to the technical field of RC oscillator correction, in particular to a method for automatically updating the frequency of an internal RC oscillator. Background Art

[0002] Generally, an oscillation source is required for the operation of a chip. The oscillation source comes from an external oscillator or a built-in oscillator. The frequency of an external oscillator is more accurate, but the cost is higher; while the cost of a built-in oscillator is lower, but the output frequency is less accurate. A built-in oscillator is usually composed of resistors and capacitors. There will be errors in the chip manufacturing process. This error will cause the resistors and capacitors to deviate, making the frequency inaccurate. In order to make the frequency of the built-in oscillator more accurate, a more accurate frequency can be obtained by fine-tuning the resistors or capacitors. For ease of adjustment, one of the resistors or capacitors is usually fixed, and only the other is adjusted. According to the amplitude and range of the desired fine-tuning, the chip will design corresponding settings for adjustment.

[0003] The traditional calibration method is to check one by one, and first set the minimum value, then detect the frequency. If the frequency is within the target range, the calibration is completed. If the frequency is not within the set range, the set value is increased by one, and then the above actions are repeated until the frequency is within the target range. The traditional calibration method has several disadvantages. When the set range increases, the calculation time of the step-by-step calibration will also increase, which has the disadvantage of long calibration time. At the same time, the step-by-step calibration method does not take into account the characteristics of the internal oscillator frequency. The set value taken is just to meet the frequency within the target range. Therefore, the calculated frequency of the set value taken has a large error with the target frequency, which has the disadvantage of low accuracy.

[0004] Other calibration methods may also have the following disadvantages: the test program needs to be burned to increase the detection time; the counting time length needs to be converted according to the target frequency; the test model cycle needs to be adjusted in conjunction with the counting time; the calculation formula is complex; the calculation range is small; the test model content is not easy to adjust; a shareable internal frequency divider needs to be added; more pins are required; the frequency is easily interfered with; and the applicability is not wide. Summary of the invention

[0005] The object of the present invention is to provide a method for automatically updating the frequency of an internal RC oscillator to solve the problems raised in the above background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solution: a method for automatically updating the frequency of an internal RC oscillator, the method comprising the following steps:

[0007] S1: Obtain the target frequency, the error allowable value and the set value correction bit, and then go to step S2;

[0008] S2: Calculate the minimum setting value and the maximum setting value by the setting value correction bit number, and then go to step S3;

[0009] S3: Perform a binary approximation operation on the minimum setting value and the maximum setting value to obtain a calculated frequency value that iteratively approaches the target frequency and its corresponding frequency correction setting value, and then go to step S4;

[0010] S4: When the obtained frequency correction setting value cannot be calculated by binary approximation method, the operation is terminated, and the multiple calculated frequency values ​​at the end of the operation and the corresponding frequency correction setting values ​​are judged, and the minimum error setting value is output, and then the process goes to S5;

[0011] S5: Compare the error of the minimum error setting value with the error allowable value and output the judgment result.

[0012] Furthermore, in step S1, the target frequency is calculated from the actual target frequency, the target frequency is the integer part of the actual target frequency in KHz, the actual target frequency is the frequency required to be output by the internal RC oscillator, the allowable error value is calculated from the target frequency and the allowable error value, and the number of correction bits of the set value is obtained from the hardware properties of the internal RC oscillator.

[0013] Furthermore, the step S3 includes the following steps:

[0014] S31: Calculate the saved minimum setting value and maximum setting value, obtain their medians, and go to step S32;

[0015] S32: Determine whether the obtained median is an integer. If not, round it up to the nearest integer and go to step S33;

[0016] S33: Write the obtained median into the chip to obtain its calculation frequency, and then go to step S34;

[0017] S34: Compare the calculated frequency with the target frequency. When the calculated frequency is greater than the target frequency, the median replaces the maximum setting value. When the calculated frequency is less than the target frequency, the median replaces the minimum setting value.

[0018] Further, the step S4 includes the following steps:

[0019] S41: When it is determined that the obtained median is an odd number and the calculated frequency obtained by writing the median into the chip is greater than the target frequency, the final set value output is equal to the minimum set value of the median in the previous step, and then go to step S42;

[0020] S42: When it is determined that the median is an odd number and the calculated frequency obtained by writing the median into the chip is less than the target frequency, the final set value output is equal to the maximum set value of the median in the previous step, and the process goes to step S43;

[0021] S43: Write the final set value into the chip to obtain its calculation frequency, calculate the calculation frequency and the target frequency to obtain the error corresponding to the median and the error corresponding to the final set value, compare the errors of the two, and output the minimum error set value, which is the optimal correction value.

[0022] Furthermore, the step S5 includes the following steps:

[0023] S51: Compare the error of the minimum error setting value with the error allowable value, and when it is determined that the error is greater than the error allowable value, output automatic correction failure;

[0024] S52: Compare the error of the minimum error setting value with the error allowable value. When it is determined that the error is less than the error allowable value, the automatic correction is judged to be successful, the minimum error setting value is output, and the operation ends.

[0025] Further, the method comprises the following steps:

[0026] S61:I 2 In standby mode, the SCL pin and SDA pin are high level. When the operation starts, the SDA pin becomes low level to generate a start signal. 2 C data transmission;

[0027] S62:I 2 C changes the SCL pin to a low level in standby mode, I 2 C has no action, and then the SCL pin becomes high level, I 2 C will return to standby mode;

[0028] S63: In standby mode, the SCL pin is changed to a low level, and after a fixed time, the SCL pin is changed to a high level again, completing a signal sent to the chip for a fixed time count.

[0029] Furthermore, the method will set a fixed time by the test machine and then set the target frequency for calculation and comparison, and the fixed time is the time for the counter to count once.

[0030] Furthermore, in the method, the pin of the fixed time of the given chip of the machine will be integrated into the SCL pin, and the method only needs the two pins SCL and SDA to realize the function.

[0031] Compared with the prior art, the beneficial effects achieved by the present invention are: the present invention operates in the calculation mode of the binary approximation method, and has the calculation advantages of the binary approximation method. The calculation method of taking the midpoint for judgment can effectively shorten the calculation time when the setting range is large compared with the traditional one-by-one inspection method. At the same time, combined with the calculation characteristics, the frequency correction accuracy can be greatly improved. The number of pins required is less than that of the traditional method, which reduces the hardware requirements. The test model is simpler to set because of the essential difference in the calculation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0033] Figure 1 It is a schematic diagram of the calculation and judgment process of the present invention;

[0034] Figure 2 This is a statistical diagram of calculations when the number of correction bits for the set value is 3;

[0035] Figure 3 is a schematic diagram of the automatic correction simulation interface of the present invention;

[0036] Figure 4 It is a schematic diagram of the automatic correction judgment simulation interface of the present invention. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] See also Figure 1-4 , the present invention provides a technical solution:

[0039] A method for automatically updating the frequency of an internal RC oscillator, the method comprising the following steps:

[0040] S1: Obtain the target frequency, the error allowable value and the set value correction bit, and then go to step S2;

[0041] S2: Calculate the minimum setting value and the maximum setting value by the setting value correction bit number, and then go to step S3;

[0042] S3: Perform a binary approximation operation on the minimum setting value and the maximum setting value to obtain a calculated frequency value that iteratively approaches the target frequency and its corresponding frequency correction setting value, and then go to step S4;

[0043] S4: When the obtained frequency correction setting value cannot be calculated by binary approximation method, the operation is terminated, and the multiple calculated frequency values ​​at the end of the operation and the corresponding frequency correction setting values ​​are judged, and the minimum error setting value is output, and then the process goes to S5;

[0044] S5: Compare the error of the minimum error setting value with the error allowable value and output the judgment result.

[0045] like Figure 2 As shown, taking the setting value correction digit as 3 as an example, the IRC characteristic curve function is F(x), the minimum setting value is 0, and the maximum setting value is 2 3 -1=7, target frequency is n KHz, F(0)<n,F(7)> n, where (3'b100), (3'b110), etc. are binary representations of numerical values.

[0046] (1) Substitute the median of 0 and 7, 4(3'b100), into the calculation to obtain the frequency value.

[0047] (2) If the calculated frequency value is greater than the target frequency value, replace 7 with 4;

[0048] If the calculated frequency value is less than the target frequency value, 0 is replaced by 4.

[0049] (3) The second median is 6 (3'b110) or 2 (3'b010).

[0050] (4) Similarly, the third median is 7 (3'b111), 5 (3'b101), 3 (3'b011), or 1 (3'b001).

[0051] (5) After calculating three times, the values ​​obtained are only adjacent odd numbers, which satisfies the condition that the median is an odd number.

[0052] (6) Compare the frequency correction setting value errors obtained from the third and fourth calculations. The smaller error is the optimal frequency correction setting value.

[0053] (7) Compare the error of the optimal frequency correction setting value with the error allowance value. When the error is less than the error allowance value, the optimal frequency correction setting value is sent to the SDA pin. When the error is greater than the error allowance value, the automatic correction judgment fails.

[0054] In step S1, the target frequency is calculated from the actual target frequency, the target frequency is the integer part of the actual target frequency in KHz, the actual target frequency is the frequency required to be output by the internal RC oscillator, the error allowance is calculated from the target frequency and the allowable error value, and the set value correction bit number is obtained from the hardware properties of the internal RC oscillator.

[0055] The step S3 comprises the following steps:

[0056] S31: Calculate the saved minimum setting value and maximum setting value, obtain their medians, and go to step S32;

[0057] S32: Determine whether the obtained median is an integer. If not, round it up to the nearest integer and go to step S33;

[0058] S33: Write the obtained median into the chip to obtain its calculation frequency, and then go to step S34;

[0059] S34: Compare the calculated frequency with the target frequency. When the calculated frequency is greater than the target frequency, the median replaces the maximum setting value. When the calculated frequency is less than the target frequency, the median replaces the minimum setting value.

[0060] The step S4 comprises the following steps:

[0061] S41: When it is determined that the obtained median is an odd number and the calculated frequency obtained by writing the median into the chip is greater than the target frequency, the final set value output is equal to the minimum set value of the median in the previous step, and then go to step S42;

[0062] S42: When it is determined that the median is an odd number and the calculated frequency obtained by writing the median into the chip is less than the target frequency, the final set value output is equal to the maximum set value of the median in the previous step, and the process goes to step S43;

[0063] S43: Write the final set value into the chip to obtain its calculation frequency, calculate the calculation frequency and the target frequency to obtain the error corresponding to the median and the error corresponding to the final set value, compare the errors of the two, and output the minimum error set value, which is the optimal correction value.

[0064] The step S5 comprises the following steps:

[0065] S51: Compare the error of the minimum error setting value with the error allowable value, and when it is determined that the error is greater than the error allowable value, output automatic correction failure;

[0066] S52: Compare the error of the minimum error setting value with the error allowable value. When it is determined that the error is less than the error allowable value, the automatic correction is judged to be successful, the minimum error setting value is output, and the operation ends.

[0067] The method comprises the following steps:

[0068] S61:I 2 In standby mode, the SCL pin and SDA pin are high level. When the operation starts, the SDA pin becomes low level to generate a start signal.2 C data transmission;

[0069] S62:I 2 C changes the SCL pin to a low level in standby mode, I 2 C has no action, and then the SCL pin becomes high level, I 2 C will return to standby mode;

[0070] S63: In standby mode, the SCL pin is changed to a low level, and after a fixed time, the SCL pin is changed to a high level again, completing a signal sent to the chip for a fixed time count.

[0071] The traditional frequency calibration method is to measure the frequency directly, which requires a pin to output the frequency. Therefore, the automatic frequency calibration requires fewer pins than the traditional frequency calibration. The final comparison result of the automatic frequency calibration requires a pin to output the result, which is sent to the SDA pin.

[0072] like Figure 3 The following is the automatic correction simulation interface, taking the setting value correction digit as 7 as an example, the content is as follows:

[0073] (1) Obtain and list the target frequencies, such as Figure 3 The value of the target frequency obtained is 16589.

[0074] (2) Obtain and list multiple frequency correction setting values, calculation frequencies, and error values, start the zeroth operation from the maximum setting value 127 and the minimum setting value 0, take the median of the maximum setting value 127 and the minimum setting value 0 as 64, run the first operation to write the decimal 64 setting value data into the chip, and simulate the generation: "TRIMDATA=0X40(100_0000), CNT=20056, ERROR=3467", where the listed frequency correction setting value numerical information includes hexadecimal and binary. The calculation frequency obtained by writing the decimal 64 setting value into the chip is 20056, which is greater than the target frequency value 16589. The error is the calculation frequency value minus the target frequency value, which is equal to 3467. Because its calculation frequency is greater than the target frequency, the decimal 64 setting value replaces the decimal 127 setting value as the maximum setting value.

[0075] The median of the maximum setting value 64 and the minimum setting value 0 is taken as 32, and the decimal 32 setting value data is written into the chip. The simulation generates: "TRIMDATA=0X20(010_0000), CNT=17494, ERROR=905". The calculated frequency obtained by writing the decimal 32 setting value into the chip is 17494, which is greater than the target frequency value 16589. The error is the calculated frequency value minus the target frequency value, which is equal to 905. Because its calculated frequency is greater than the target frequency, the decimal 32 setting value replaces the decimal 64 setting value as the maximum setting value.

[0076] The median of the maximum setting value 32 and the minimum setting value 0 is taken as 16, and the decimal 16 setting value data is written into the chip. The simulation generates: "TRIMDATA=0X10(001_0000), CNT=16180, ERROR=-409". The calculated frequency obtained by writing the decimal 16 setting value into the chip is 16180, which is less than the target frequency value 16589. The error is the calculation frequency value minus the target frequency value, which is -409. Because its calculation frequency is less than the target frequency, the decimal 16 setting value replaces the decimal 0 setting value to become the minimum setting value.

[0077] The median of the maximum setting value 32 and the minimum setting value 16 is taken as 24, and the decimal setting value data of 24 is written into the chip. The simulation generates: "TRIMDATA=0X18(001_1000), CNT=16840, ERROR=251". The calculated frequency obtained by writing the decimal setting value of 24 into the chip is 16840. The calculated frequency is greater than the target frequency value of 16589. The error is the calculation frequency value minus the target frequency value, which is equal to 251. Because its calculated frequency is greater than the target frequency, the decimal setting value of 24 replaces the decimal setting value of 32 to become the maximum setting value.

[0078] The median of the maximum setting value 24 and the minimum setting value 16 is taken as 20, and the decimal setting value data of 20 is written into the chip. The simulation generates: "TRIMDATA=0X14(001_0100), CNT=16511, ERROR=-78". The calculated frequency obtained by writing the decimal setting value of 20 into the chip is 16511. The calculated frequency is less than the target frequency value 16589. The error is the arithmetic subtraction of the target frequency value from the calculated frequency value, which is -78. Because its calculated frequency is less than the target frequency, the decimal setting value of 20 replaces the decimal setting value of 16 to become the minimum setting value.

[0079] The median of the maximum setting value 24 and the minimum setting value 20 is taken as 22, and the decimal setting value data of 22 is written into the chip. The simulation generates: "TRIMDATA=0X16(001_0110), CNT=16682, ERROR=93". The calculated frequency obtained by writing the decimal setting value of 22 into the chip is 16682. The calculated frequency is greater than the target frequency value of 16589. The error is the calculation frequency value minus the target frequency value, which is equal to 93. Because its calculated frequency is greater than the target frequency, the decimal setting value of 22 replaces the decimal setting value of 24 to become the maximum setting value.

[0080] The median of the maximum setting value 22 and the minimum setting value 20 is taken as 21, and the decimal setting value data of 21 is written into the chip. The simulation generates: "TRIMDATA=0X15(001_0101), CNT=16594, ERROR=5". The calculated frequency obtained by writing the decimal setting value 21 into the chip is 16594. The calculated frequency is greater than the target frequency value 16589. The error is the calculation frequency value minus the target frequency value, which is equal to 5. Because the decimal setting value of 21 is an odd number, the loop operation ends and the minimum setting value 20 will be written into the chip. The simulation generates: "TRIMDATA=0X14(001_0100), CNT=16512, ERROR=-77". The calculated frequency obtained by writing the minimum setting value 20 into the chip is 16512. The error is the calculation frequency value minus the target frequency value, which is equal to -77.

[0081] (3) Compare the error values, obtain and list the frequency correction setting value with the smallest error value, such as Figure 3 The figure shows a comparison of the absolute value of the error between the decimal set value 21 and the minimum set value 20. The error of the decimal set value 21 is smaller, and the error value is 5. The decimal set value 21 is output in hexadecimal.

[0082] like Figure 4 The following is the automatic correction judgment simulation interface:

[0083] (1) Obtain and list the target frequencies, such as Figure 4 The target frequency value shown is 16589.

[0084] (2) Obtain and list the error tolerance values, such as Figure 4 The error tolerance shown is 165.

[0085] (3) Obtain and list the optimal frequency correction setting value, calculated frequency, and error value derived from the automatic correction simulation, such as Figure 4 The displayed content is: "TRIMDATA=0X15(001_0101), CNT=16594, ERROR=5".

[0086] (4) Compare the error value with the allowable error value, output the error value and the judgment result, such as Figure 4 The judgment error value 5 shown is less than the allowable error value 165, the output error value is 5, and the output judgment command is normal.

[0087] The automatic calibration judgment only needs to be performed once, and the judgment result is sent to the SDA pin.

[0088] The method externally gives a fixed time of 1 ms, and then sets a target frequency for calculation and comparison. Compared with other traditional methods, this method of setting the target frequency is intuitive and does not require calculation.

[0089] The hardware structure of the method is as follows: 2 C serial bus type only needs two pins, SCL and SDA, to realize the transmission of clock signal and data signal, and has the advantage of low hardware requirements.

[0090] The working principle of the present invention is as follows: a target frequency obtained by calculation, a correction bit number of a set value, and a calculated frequency obtained by writing the median of a maximum set value and a minimum set value into a chip are subjected to a binary approximation operation, a correction set value closer to the target frequency and its corresponding calculation frequency and error are obtained by iterative calculation, the errors corresponding to multiple correction set values ​​at the end of the binary approximation operation are taken, the error sizes are compared, the correction set value with the minimum error is obtained, the minimum error is compared with the error allowable value, the comparison result is sent to the SDA pin, and the automatic update of the internal RC oscillator frequency is completed.

[0091] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0092] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for automatically updating the frequency of an internal RC oscillator, characterized in that: The method comprises the following steps: S1: Obtain the target frequency, the error allowable value and the set value correction bit, and then go to step S2; S2: Calculate the minimum setting value and the maximum setting value by the setting value correction bit number, and then go to step S3; S3: Perform a binary approximation operation on the minimum setting value and the maximum setting value to obtain a calculated frequency value that iteratively approaches the target frequency and its corresponding frequency correction setting value, and then go to step S4; S4: When the obtained frequency correction setting value cannot be calculated by binary approximation method, the operation is terminated, and the multiple calculated frequency values ​​at the end of the operation and the corresponding frequency correction setting values ​​are judged, and the minimum error setting value is output, and then the process goes to S5; S5: Compare the error of the minimum error setting value with the error allowable value and output the judgment result; The step S3 comprises the following steps: S31: Calculate the saved minimum setting value and maximum setting value, obtain their medians, and go to step S32; S32: Determine whether the obtained median is an integer. If not, round it up to the nearest integer and go to step S33; S33: Write the obtained median into the chip to obtain its calculation frequency, and then go to step S34; S34: Compare the calculated frequency with the target frequency. When the calculated frequency is greater than the target frequency, the median replaces the maximum setting value. When the calculated frequency is less than the target frequency, the median replaces the minimum setting value.

2. The method for automatically updating the frequency of an internal RC oscillator according to claim 1, characterized in that: In step S1, the target frequency is calculated from the actual target frequency, the target frequency is the integer part of the actual target frequency in KHz, the actual target frequency is the frequency required to be output by the internal RC oscillator, the error allowance is calculated from the target frequency and the allowable error value, and the set value correction bit number is obtained from the hardware properties of the internal RC oscillator.

3. The method for automatically updating the frequency of an internal RC oscillator according to claim 1, characterized in that: The step S4 comprises the following steps: S41: When it is determined that the obtained median is an odd number and the calculated frequency obtained by writing the median into the chip is greater than the target frequency, the final set value output is equal to the minimum set value of the median in the previous step, and then go to step S42; S42: When it is determined that the median is an odd number and the calculated frequency obtained by writing the median into the chip is less than the target frequency, the final set value output is equal to the maximum set value of the median in the previous step, and the process goes to step S43; S43: Write the final set value into the chip to obtain its calculation frequency, calculate the calculation frequency and the target frequency to obtain the error corresponding to the median and the error corresponding to the final set value, compare the errors of the two, and output the minimum error set value, which is the optimal correction value.

4. The method for automatically updating the frequency of an internal RC oscillator according to claim 1, characterized in that: The step S5 comprises the following steps: S51: Compare the error of the minimum error setting value with the error allowable value, and when it is determined that the error is greater than the error allowable value, output automatic correction failure; S52: Compare the error of the minimum error setting value with the error allowable value. When it is determined that the error is less than the error allowable value, the automatic correction is judged to be successful, the minimum error setting value is output, and the operation ends.

5. The method for automatically updating the frequency of an internal RC oscillator according to claim 1, characterized in that: The method comprises the following steps: S61:I 2 In standby mode, the SCL pin and SDA pin are high level. When the operation starts, the SDA pin becomes low level to generate a start signal. 2 C data transmission; S62:I 2 C in standby mode, the SCL pin becomes low level, I 2 C has no action, and then the SCL pin becomes high level, I 2 C will return to standby mode; S63: In standby mode, the SCL pin is changed to a low level, and after a fixed time, the SCL pin is changed to a high level again, completing a signal sent to the chip for a fixed time count.

6. The method for automatically updating the frequency of an internal RC oscillator according to claim 5, characterized in that: The method will set a fixed time by the test machine and then set the target frequency for calculation and comparison. The fixed time is the time for the counter to count once.

7. The method for automatically updating the frequency of an internal RC oscillator according to claim 5, characterized in that: In the method, the pin of the fixed time of the given chip of the machine will be integrated into the SCL pin. This method only needs the SCL and SDA pins to realize the function.

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