CN104796118A - Method for breaking through limited pwm (pulse width modulation) output of MCU (micro control unit) hardware - Google Patents
Method for breaking through limited pwm (pulse width modulation) output of MCU (micro control unit) hardware Download PDFInfo
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- CN104796118A CN104796118A CN201510211221.8A CN201510211221A CN104796118A CN 104796118 A CN104796118 A CN 104796118A CN 201510211221 A CN201510211221 A CN 201510211221A CN 104796118 A CN104796118 A CN 104796118A
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Abstract
The invention discloses a method for breaking through limited pwm (pulse width modulation) output of MCU (micro control unit) hardware. The method is characterized by including the following steps: S1, initializing clock configuration, and configuring an 8-bit continuous clock overflow interrupt in the MCU; S2, performing normal operation for set time prior to appearing of one interrupt; S3, judging whether an I/O (input/output) output flag is true or not, if yes, reloading low-level time in pwm to a clock timer, setting the I/O output flag as false, outputting low level by an I/O port, and then repeating the step S2; if the I/O output flag is false, reloading high-level time in the pwm to the clock timer, setting the I/O output flag as true, outputting high level by the I/O port, and then repeating the step S2. Product upgrade and development cycle is short, change of a hardware circuit, addition of a high-speed external crystal oscillator or replacement for a high-speed MCU is not needed, and cost is lowered.
Description
Technical field
The present invention relates to pulse-width modulation field, particularly relate to a kind of method that restriction breaking through MCU hardware exports pwm.
Background technology
In current various electronic equipment, the perfect in shape and function of MCU, wherein just comprises pwm output function; The output function of its MCU hardware supports pwm, only needs to carry out pwm configuration to current MCU, and the pwm that can obtain corresponding frequency exports.
But the crystal oscillator selected for this MCU and electronic circuit limit the frequency that this MCU hardware pwm exports, and in order to improve the frequency of the output of pwm, existing technology has three kinds:
(1) change hardware circuit, pwm delivery outlet is changed to the outlet of other pwm function numbers.Defect is: product up-gradation change circuit and software carry out simultaneously, and the upgrading construction cycle is long, and negative value is many;
(2) add high speed outer crystal oscillator, pwm output frequency is increased.Defect is: need upgrade circuit and most of software merit rating, and the upgrading construction cycle is long, and product cost raises, and negative value is many;
(3) more high speed MCU is changed.Defect is: product cost raises, and software is developed again, and the cycle is long.
Summary of the invention
The object of this invention is to provide a kind of method that restriction breaking through MCU hardware exports pwm, promoting pwm output frequency when increasing hardware unit and circuit structure.
Technical scheme of the present invention is a kind of method that restriction breaking through MCU hardware exports pwm, comprises the steps:
S1, initialization clock configure, and the continuous print clock configuring 8 in MCU overflows interruption;
S2, normally to run, after the time of setting, occur an interruption; And
S3, judge whether I/O output identification is true, when I/O output identification is true time, in heavily loaded pwm, low level time is to clock timer, and I/O output identification is set to vacation, I/O mouth output low level, then repeats step S2; When I/O output identification is fictitious time, in heavily loaded pwm, high level time is to clock timer, and I/O output identification is set to very, and I/O mouth exports high level, then repeats step S2.
The technical program adopts 8 bit clock timers to carry out simulation pwm output function, makes it possible to I/O mouth adjustable duty cycle number Dc in MCU to set arbitrarily.As by Dc=100, so Dc<255; Frequency is raised, breaches the pwm output function of original MCU hardware.The product up-gradation construction cycle is short, does not need change hardware circuit, adds high speed outer crystal oscillator or change high speed MCU, reduce cost.
Further, in step S2, the time of described setting meets following formula:
Tx=255*t
In formula, Tx represents the distance next time of interrupting, and t represents the instruction cycle of MCU.When program runs to time Tx, there is an interruption; When off-duty is to Tx, continue to run.
Further, in step S3, in heavily loaded pwm, low level time meets following formula:
Tl=（255-Dc+Dd）*t
In formula, Tl represents low level time in pwm, and t represents the instruction cycle of MCU, and Dc represents adjustable duty cycle number, and Dd represents the numerical value that duty ratio is corresponding.
Further, in step S3, in heavily loaded pwm, high level time meets following formula:
Th=（255-Dd）*t
In formula, Th represents high level time in pwm, and t represents the instruction cycle of MCU, and Dd represents the numerical value that duty ratio is corresponding.
Further, the cycle of the final stable output of I/O mouth of MCU is the pwm waveform of T, and described cycle T meets formula:
T=Th+Tl=Dc*t （1）
In formula, T represents the cycle of pwm, and t represents the MCU instruction cycle, and Dc represents adjustable duty cycle number;
The duty ratio of described pwm waveform is (Dd/Dc) * 100%;
Can draw according to formula (1), the frequency that the I/O mouth of MCU finally exports pwm waveform meets formula:
Fpwm=1/T=1/(Dc*t)
In formula, Dc represents adjustable duty cycle number, and t represents the instruction cycle of MCU
Beneficial effect: by adopting 8 bit clock timers to carry out simulation pwm output function, makes it possible to I/O mouth adjustable duty cycle number Dc in MCU to set arbitrarily, frequency is raised, breaches the pwm output function of original MCU hardware.The product up-gradation construction cycle is short, does not need change hardware circuit, adds high speed outer crystal oscillator or change high speed MCU, reduce cost.
Accompanying drawing explanation
Fig. 1 is the workflow diagram of an embodiment of the present invention.
Embodiment
Below in conjunction with accompanying drawing, preferably embodiment of the present invention is described in further detail:
See Fig. 1, a kind of restriction breaking through MCU hardware exports the method for pwm, comprises the steps:
S1, initialization clock configure, and the continuous print clock configuring 8 in MCU overflows interruption;
S2, normally to run, after the time of setting, occur an interruption; And
S3, judge whether I/O output identification is true, when I/O output identification is true time, in heavily loaded pwm, low level time is to clock timer, and I/O output identification is set to vacation, I/O mouth output low level, then repeats step S2; When I/O output identification is fictitious time, in heavily loaded pwm, high level time is to clock timer, and I/O output identification is set to very, and I/O mouth exports high level, then repeats step S2.
In step S2, the time of described setting meets following formula:
Tx=255*t
In formula, Tx represents the distance next time of interrupting, and t represents the instruction cycle of MCU.When program runs to time Tx, there is an interruption; When off-duty is to Tx, continue to run.
In step S3, in heavily loaded pwm, low level time meets following formula:
Tl=（255-Dc+Dd）*t
In formula, Tl represents low level time in pwm, and t represents the instruction cycle of MCU, and Dc represents adjustable duty cycle number, and Dd represents the numerical value that duty ratio is corresponding.
In step S3, in heavily loaded pwm, high level time meets following formula:
Th=（255-Dd）*t
In formula, Th represents high level time in pwm, and t represents the instruction cycle of MCU, and Dd represents the numerical value that duty ratio is corresponding.
The cycle of the final stable output of I/O mouth of MCU is the pwm waveform of T, and described cycle T meets formula:
T=Th+Tl=Dc*t （1）
In formula, T represents the cycle of pwm, and t represents the MCU instruction cycle, and Dc represents adjustable duty cycle number;
The duty ratio of described pwm waveform is (Dd/Dc) * 100%;
Can draw according to formula (1), the frequency that the I/O mouth of MCU finally exports pwm waveform meets formula:
Fpwm=1/T=1/(Dc*t)
In formula, Dc represents adjustable duty cycle number, and t represents the instruction cycle of MCU.
In the present embodiment, MCU model is MB95F564K, t=0.25, supposes Dd=50, Dc=100, and so the duty ratio of pwm waveform is:
50/100*100=50%，
The frequency that the I/O mouth of MCU finally exports pwm waveform is:
(1/100*0.25)MHz=40KHz。
Therefore, in software by 50 assignment to Dd, the duty ratio that this MCU just can be made to export a 40KHz is the pwm waveform of 50%.
The present embodiment adopts 8 bit clock timers to carry out simulation pwm output function, makes it possible to I/O mouth adjustable duty cycle number Dc in MCU to set arbitrarily.As by Dc=100, so Dc<255; Frequency is raised, breaches the pwm output function of original MCU hardware.The product up-gradation construction cycle is short, does not need change hardware circuit, adds high speed outer crystal oscillator or change high speed MCU, reduce cost.
Above content is in conjunction with concrete preferred implementation further description made for the present invention, can not assert that specific embodiment of the invention is confined to these explanations.For general technical staff of the technical field of the invention, without departing from the inventive concept of the premise, some simple deduction or replace can also be made, all should be considered as belonging to protection scope of the present invention.
Claims (5)
1. the restriction breaking through MCU hardware exports a method of pwm, it is characterized in that, comprises the steps:
S1, initialization clock configure, and the continuous print clock configuring 8 in MCU overflows interruption;
S2, normally to run, after the time of setting, occur an interruption; And
S3, judge whether I/O output identification is true, when I/O output identification is true time, in heavily loaded pwm, low level time is to clock timer, and I/O output identification is set to vacation, I/O mouth output low level, then repeats step S2; When I/O output identification is fictitious time, in heavily loaded pwm, high level time is to clock timer, and I/O output identification is set to very, and I/O mouth exports high level, then repeats step S2.
2. the restriction of breakthrough MCU hardware according to claim 1 exports the method for pwm, and it is characterized in that, in step S2, the time of described setting meets following formula:
Tx=255*t
In formula, Tx represents the distance next time of interrupting, and t represents the instruction cycle of MCU.
3. the restriction of breakthrough MCU hardware according to claim 2 exports the method for pwm, and it is characterized in that, in step S3, in heavily loaded pwm, low level time meets following formula:
Tl=（255-Dc+Dd）*t
In formula, Tl represents low level time in pwm, and t represents the instruction cycle of MCU, and Dc represents adjustable duty cycle number, and Dd represents the numerical value that duty ratio is corresponding.
4. the restriction of breakthrough MCU hardware according to claim 3 exports the method for pwm, and it is characterized in that, in step S3, in heavily loaded pwm, high level time meets following formula:
Th=（255-Dd）*t
In formula, Th represents high level time in pwm, and t represents the instruction cycle of MCU, and Dd represents the numerical value that duty ratio is corresponding.
5. the restriction of breakthrough MCU hardware according to claim 4 exports the method for pwm, and it is characterized in that, the cycle of the final stable output of I/O mouth of MCU is the pwm waveform of T, and described cycle T meets formula:
T=Th+Tl=Dc*t （1）
In formula, T represents the cycle of pwm, and t represents the MCU instruction cycle, and Dc represents adjustable duty cycle number;
The duty ratio of described pwm waveform is (Dd/Dc) * 100%;
Can draw according to formula (1), the frequency that the I/O mouth of MCU finally exports pwm waveform meets formula:
Fpwm=1/T=1/(Dc*t)
In formula, Dc represents adjustable duty cycle number, and t represents the instruction cycle of MCU.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105446417A (en) * | 2014-08-21 | 2016-03-30 | Tcl集团股份有限公司 | Method and system for acquiring high-precision timing signal |
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| US6995592B2 (en) * | 2003-11-06 | 2006-02-07 | Stmicroelectronics Pvt. Ltd. | Method and system for generating variable frequency cyclic waveforms using pulse width modulation |
| US20060104343A1 (en) * | 2004-10-29 | 2006-05-18 | Stmicroelectronics Pvt. Ltd. | PWM generator providing improved duty cycle resolution |
| CN1996729A (en) * | 2006-12-23 | 2007-07-11 | 深圳市拓邦电子科技股份有限公司 | Multi-channel PWM generation system and method |
| US7348755B2 (en) * | 2003-12-18 | 2008-03-25 | The Boeing Company | Time sliced DSP operation for very high frequency pulse width modulated controllers |
| CN103312300A (en) * | 2013-06-24 | 2013-09-18 | 哈尔滨工业大学 | Pulse-width modulation (PWM) signal generator based on field programmable gate array (FPGA) |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
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| US6995592B2 (en) * | 2003-11-06 | 2006-02-07 | Stmicroelectronics Pvt. Ltd. | Method and system for generating variable frequency cyclic waveforms using pulse width modulation |
| US7348755B2 (en) * | 2003-12-18 | 2008-03-25 | The Boeing Company | Time sliced DSP operation for very high frequency pulse width modulated controllers |
| US20060104343A1 (en) * | 2004-10-29 | 2006-05-18 | Stmicroelectronics Pvt. Ltd. | PWM generator providing improved duty cycle resolution |
| CN1996729A (en) * | 2006-12-23 | 2007-07-11 | 深圳市拓邦电子科技股份有限公司 | Multi-channel PWM generation system and method |
| CN103312300A (en) * | 2013-06-24 | 2013-09-18 | 哈尔滨工业大学 | Pulse-width modulation (PWM) signal generator based on field programmable gate array (FPGA) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105446417A (en) * | 2014-08-21 | 2016-03-30 | Tcl集团股份有限公司 | Method and system for acquiring high-precision timing signal |
| CN105446417B (en) * | 2014-08-21 | 2018-07-27 | Tcl集团股份有限公司 | A kind of method and system obtaining high precision timing signal |
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Address after: 518000 Guangdong province Shenzhen Guangming New District Gongming street Gongming South Avenue Geya Technology Building 3 building 1-4 layer Patentee after: Shenzhen Zhenbang intelligent Polytron Technologies Inc Address before: 518000 Guangdong, Nanshan District, Taoyuan, Longjing street, industrial zone, building A, building 2, building A, building on the ground floor, building B, building, building 6, building C, block B, building, building No. 3 Patentee before: SHENZHEN ZHENBANG INTELLIGENT TECHNOLOGY CO., LTD. |
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