CN104698286B - A kind of PWM ripple acquisition methods based on timer - Google Patents

Abstract

The present invention is a timer-based PWM wave collection method, the steps of which are as follows: 1: set a timer as a cycle counting work mode, and trigger a clock interruption every cycle; 2: set the timer for PWM wave collection as high Level-triggered downcounting mode of operation, the input of the PWM wave acquisition timer is connected to the PWM wave signal to be collected; 3: Write an interrupt service function to respond to the clock interrupt after each cycle counting ends. The timer-based PWM wave acquisition method of the present invention adopts a high-level trigger timer counting instead of a pulse capture acquisition method, even if the signal appears such as glitches or other jumps, it has almost no effect on the acquisition results, thereby greatly Improve the anti-interference ability of PWM acquisition.

Description

A Timer-Based PWM Wave Acquisition Method

technical field

The invention provides a timer-based PWM wave acquisition method, which relates to a timer-based pulse width length modulation signal PWM wave acquisition method, and proposes a timer-based PWM wave acquisition method. This timer-based PWM wave acquisition method can be extended to various types of timers to realize the acquisition of PWM signals, and is applicable to various industrial control fields. In the present invention, the CDT2000 board is used as an example to explain the example. The collected PWM wave is a 14ms cycle PWM wave used to control the action of the steering gear, and the pulse width length ranges from 1.1 to 1.9ms.

Background technique

PWM wave (PWM, that is, Pulse Width Modulation, pulse width modulation) is a mature industrial control signal, which is widely used in industrial control such as motor speed control and actuator stroke control. It uses digital output to control analog circuits. A very effective technique of control.

The waveform diagram of the PWM wave is shown in Figure 1, t _c is the pulse period, t ₁ and t ₂ are the pulse width lengths representing the effective information of the PWM wave. The PWM wave in the present invention is derived from the requirement for the actuation control of the steering gear, and it is necessary to collect a pulse width modulation signal with a period of 14 ms and a pulse width ranging from 1.1 to 1.9 ms.

The acquisition of PWM wave is to use some equipment to realize the measurement of the pulse width length of PWM wave.

In the traditional PWM wave acquisition method, the timing of the rising and falling edges of the pulse width signal is recorded separately, and then the difference between the two timings is used to obtain the pulse width length. The disadvantage of this method is that when the voltage of the pulse width signal is unstable or has burrs, the judgment of the rising edge and falling edge will be wrong, resulting in an error in signal acquisition.

The PWM wave acquisition method used in the present invention uses the PWM wave signal as the trigger source of the timer, sets the timer as a high-level trigger, and then adopts a designed interrupt service function to regularly read the count value of the timer. Use the variation of the count value in the timer to calculate the duration of the high level, so that it will not be disturbed by voltage instability and glitches, and has strong anti-interference ability.

Contents of the invention

<1> Purpose of the invention

The purpose of the present invention is to design a method for collecting PWM waves based on a timer. With the timer as the main hardware device, through certain physical connections and coding of interrupt service functions, PWM waves applicable to various cycles and pulse widths can be realized. collection of waves.

<2>Technical solution

A kind of PWM wave acquisition method based on timer of the present invention, its steps are as follows:

Step 1: Set a timer to work in cycle counting mode, and trigger a clock interrupt every cycle;

Step 2: Set the timer used for PWM wave acquisition as the working mode of high level triggering down counting, and the input terminal of the PWM wave acquisition timer is connected with the PWM wave signal to be collected;

Step 3: Write an interrupt service function to respond to the clock interrupt after each cycle count ends. Among them, the "high-level trigger down-counting working mode" described in step 2 is another working mode that can be set for the timer. The function of this working mode is: when the PWM wave collects the input of the timer When the high level of the PWM wave signal arrives, it will trigger the timer to perform self-decrement, and when the low level arrives, it will end the self-decrement.

Among them, the "cycle counting working mode" described in step 1 is a working mode of the timer that can be set. Given a set value, it will decrease from this value to zero, and then return to This value continues to decrease by itself, and it goes round and round, the cycle count period = set value / cycle count timer clock frequency; each time when the count decreases to zero, a clock interrupt is triggered; in order to realize the acquisition of PWM waves, the cycle count period must be less than PWM One-half of the minimum duration of the wave low level, so as to ensure that the "interrupt service function" described in step 3 can read the count value when the "PWM wave acquisition timer" described in step 2 stops counting .

Among them, the "interrupt service function" described in step 3 is a function called by triggering an interrupt at the end of each cycle counting timer cycle, and its function is: to read a PWM wave every cycle counting timer cycle Collect the count value of the timer, and judge the count value of the PWM wave acquisition timer for two adjacent cycles; if the count values of the PWM wave acquisition timer for two consecutive cycles are equal and not equal to the initial count value, it indicates that the pulse is high The level has ended, the pulse width length = (the initial count value of the PWM wave acquisition timer - the count end value of the PWM wave acquisition timer) / the clock frequency of the PWM wave acquisition timer, read the value of the pulse width length, and convert the PWM wave The collection timer is reloaded; otherwise, no processing is done.

The timing diagram of collecting PWM waves with a timer is shown in Figure 2.

<3>Advantages and efficacy

The timer-based PWM wave acquisition method uses a high-level trigger timer count instead of a pulse capture acquisition method, even if the signal appears such as glitches or other jumps, it has almost no effect on the acquisition results, thereby greatly improving The anti-interference ability of PWM acquisition.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings.

Fig. 1 is a schematic diagram of the waveform of a PWM wave.

Fig. 2 is a timing diagram of collecting PWM waves with a timer, and there are explanations of related variables in the remarks; wherein, 1, the counting cycle T of the cycle counting timer must be less than 1/2 of the maximum value of the low-level length of the PWM wave _; 2. If the count value that is the same and not equal to T _max is read in two consecutive interrupts, it is considered that the high level has ended; 3. In the interrupt that judges the end of the high level, read the PWM wave pulse width t ₁ =(T _max -T ₁ )/f _{timer clock frequency} , the count value of the reload PWM wave acquisition timer is T _max .

Fig. 3 is the circuit and signal connection diagram of PWM wave acquisition using the timer function of CDT2000 in the application example.

Fig. 4 is the timing diagram of PWM wave acquisition using the timer function of CDT2000 in the application example.

Fig. 5 is a flow chart of the method of the present invention.

detailed description

Implementation steps

As shown in Figure 1-5, a kind of PWM wave acquisition method based on timer of the present invention, as shown in Figure 5, its steps are as follows:

Step 1: Set a timer to work in cycle counting mode, trigger a clock interrupt every cycle, and the cycle count cycle must be less than half of the minimum duration of PWM wave low level.

Step 2: Set the timer used for PWM wave acquisition to the working mode of high-level trigger downcounting and rising edge trigger counting overload, and the input terminal of the PWM wave acquisition timer is connected to the PWM wave signal to be collected.

Step 3: Write the interrupt service function, and respond to the clock interrupt after each cycle counts; the interrupt service function reads the count value of the PWM wave acquisition timer once per cycle, and judges the timer value of two adjacent cycles; When the values of the two cycles are equal and not equal to the initial count value, it indicates that the pulse high level has ended, the pulse width length = (initial count value - count end value) / timer clock frequency, read the pulse width length value, and PWM wave acquisition timer overload.

Applications

The example explained below comes from an actual application case. The CDT2000 board is used as the timer device, and the PC/104 embedded computer is used to realize the response of the interrupt service function. In this case, 6 channels of PWM waves need to be collected. The 6 channels of PWM collected are all from the remote control signals of the Futaba receiver, of which 1 channel is the mode switching signal, and 5 channels of PWM waves are the original servo control signals.

The PWM wave to be collected is a pulse width modulation signal with a period of 14ms and a pulse width range of 1.1 to 1.9ms.

The specific method is as follows:

1. Timer working mode setting

The four 82C54 timing controllers of the CDT2000 board each have three independent timers, and a total of 12 independent timers are obtained, and only seven of them are used for PWM wave acquisition, as shown in Figure 4. The connection and working mode settings of each timer are described as follows:

Timer 1-0: cycle counting with 2ms as cycle and generate interrupt.

Timer 3-0~Timer 4-2: start counting when GATE port is high level, and stop counting when low level.

Among them, timers 1-0 are triggered timers as interrupt service functions, and the working cycle is set to 2ms, that is, the initial count value of each cycle is set to 16000.

2. Interrupt service function function description

The principle of PWM wave acquisition in the interrupt service function is expressed as follows (see Figure 5 for the timing diagram of PWM wave acquisition):

1) Read the count value of PWM acquisition timer 3-0～timer 4-2 with a period of 2ms;

2) If the counting results of two consecutive adjacent counts are not 65535 and equal, then record the count value as T, then the pulse width of the PWM wave is t=(65535-T)/(8×10 ⁶ ), and the timer reload is max(65535);

3) If the counting results of two consecutive adjacent counts are not equal, no processing will be done.

Claims (4)

1. a kind of PWM ripple acquisition methods based on timer, it is characterised in that：Its step is as follows：

Step one：It is cycle count mode of operation to set a timer, and each cycle triggers a tick interrupt；

Step 2：It is provided for the timer of PWM ripples collection and triggers the mode of operation that subtrahend is counted, the collection of PWM ripples for high level The input of timer is connected with the PWM ripple signals to be gathered；

Step 3：Interruption service function is write, tick interrupt is responded after each cycle count terminates.

2. a kind of PWM ripple acquisition methods based on timer according to claim 1, it is characterised in that：In step 2 Described " mode of operation that high level triggering subtrahend is counted ", is another mode of operation that can be set of timer, the work The function of pattern is：Timer can be triggered when the high level that the input that PWM ripples gather timer is PWM ripple signals arrives to enter Terminate to subtract certainly when row subtracts certainly, low level arrives.

3. a kind of PWM ripple acquisition methods based on timer according to claim 2, it is characterised in that：In step one Described " cycle count mode of operation ", is a kind of mode of operation that can be configured of timer, gives a setting value, it It can then turn again to this value from this value from reducing to zero and continue, from subtracting, to go round and begin again, cycle count period=setting value/ Cycle count timer clock frequency；Every time a tick interrupt is triggered when counting and reducing to zero certainly；In order to realize adopting for PWM ripples Collection, cycle count period is necessarily less than 1/2nd of PWM ripple low duration minimum values, so just can ensure that step 3 Described in " interruption service function " " the PWM ripples gather timer " that can read described in step 2 count counting when stopping Value.

4. a kind of PWM ripple acquisition methods based on timer according to claim 1, it is characterised in that：In step 3 Described " interruption service function ", is that a called letter is interrupted in triggering at the end of each cycle count timer period Count, its function is：Each cycle count timer period reads the count value that a PWM ripple gathers timer, judges adjacent two The PWM ripples in individual cycle gather the count value of timer；If the count value of the PWM ripples collection timer in continuous two cycles is equal And when being not equal to initial count value, show that pulse high level is over, pulsewidth length=(PWM ripples gather the first of timer Beginning count value-PWM ripple gathers the counting end value of timer)/PWM ripples collection timer clock frequency, reads pulsewidth length Numerical value, and PWM ripples are gathered into timer heavy duty；Otherwise it is without any processing.