[STC15 library function hands-on notes] 7. PCA and PWM

STC Experiment Box 4

IAP15W4K58S4

Keil uVision V5.29.0.0

PK51 Prof.Developers Kit Version:9.60.0.0

Hard Knowledge

Hardware knowledge

       Excerpted from "STC15 Series MCU Device Manual"

       Some STC15 series MCUs integrate 3-channel programmable counter array (CCP/PCA) modules (STC15W4K32S4 series MCUs have only 2-channel CCP/PCA), which can be used for software timer, external pulse capture, high-speed pulse output and pulse width modulation (PWM) output.

       The following table summarizes the STC15 series MCU models that integrate CCP/PCA/PM functions:

       In the above table, √ indicates that the corresponding series has the corresponding function.

Structure of CCP/PWM/PCA module

       Some MCUs in the STC15 series have 3-channel programmable counter arrays CCP/PCA/PWM (CCP/PCA/PWM can be set to switch from port P1 to port P2 to port P3 through the AUXR1/P_SW1 register).

       The PCA contains a special 16-bit timer with three 16-bit capture/compare modules connected to it, as shown in the figure below.

       Each module can be programmed to work in 4 modes: rising/falling edge capture, software timer, high-speed pulse output or modulated pulse output.

       The 16-bit PCA timer/counter is the common time base for the three modules, and its structure is shown in the figure below.

Software knowledge

       Excerpted from "STC Library Function Usage Reference"

PCA initialization function

PCA_Init

PCA_id: Select the PCA channel to initialize:

The definition of PCA_InitTypeDef is found in the file "PCA.H".

typedef struct

{

u8 PCA_IoUse;

u8 PCA_Clock; 

u8 PCA_Mode; 

u8 PCA_PWM_Wide;

u8 PCA_Interrupt_Mode; 

u8 PCA_Polity;

u16 PCA_Value;

} PCA_InitTypeDef;

PCA_IoUse: Select the IO used by PCA: the value when initializing PCA_Counter, ignored when initializing PCA0~PCA2

PCA_Clock: Select the clock used by PCA: the value used when initializing PCA_Counter, ignored when initializing PCA0~PCA2

PCA_Mode: Set the working mode of the PCA channel: the value when initializing PCA0~PCA2, ignored when initializing PCA_Counter

PCA_PWM_Wide: Set the PWM width when the PCA channel works in PWM mode: Initialize the value of PCA0~PCA2 when working in PWM mode, ignore when initializing PCA_Counter or other modes of PCA channel

PCA_Interrupt_Mode: interrupt enable or disable: value when initializing PCA0~PCA2, ignored when initializing PCA_Counter

Note: The above parameters can be combined as follows:

PCA_InitStructure.PCA_Interrupt_Mode = PCA_Fall_Active | ENABLE; //Falling edge interrupt, enable interrupt.

PCA_InitStructure.PCA_Interrupt_Mode = PCA_Rise_Active | ENABLE; //Rising edge interrupt, enable interrupt.

PCA_InitStructure.PCA_Interrupt_Mode = PCA_Rise_Active | PCA_Fall_Active | ENABLE; //Rising edge and falling edge interrupts, enable interrupts.

If | DISABLE is used afterwards, the interrupt is disabled.

PCA_Polity: Interrupt priority: value taken when initializing PCA_Counter, ignored when initializing PCA0~PCA2

PCA_Value: Set the initial value of the PCA channel. The value used when initializing PCA0~PCA2, ignored when initializing PCA_Counter

PWM update duty cycle function

UpdatePwm

test program

PWM mode generates PWM signal

The UpdatePwm function in PCA.c is commented out by default and needs to be uncommented:

main.c

#include "./Drivers/config.h"

#include "./Drivers/delay.h"

#include "./Drivers/GPIO.h"

#include "./Drivers/PCA.h"

void GPIO_config(void)

{

GPIO_InitTypeDef GPIO_InitStructure; //Structure definition

GPIO_InitStructure.Mode = GPIO_OUT_PP; //Specify IO input or output mode, GPIO_PullUp, GPIO_HighZ, GPIO_OUT_OD, GPIO_OUT_PP

GPIO_InitStructure.Pin = GPIO_Pin_5 | GPIO_Pin_6; //Specify the IO to be initialized, or operation

GPIO_Inilize(GPIO_P2, &GPIO_InitStructure); //P2.5 and P2.6 are initialized as push-pull output

}

void PCA_config(void)

{

PCA_InitTypeDef PCA_InitStructure;

PCA_InitStructure.PCA_Mode     = PCA_Mode_PWM; //PCA_Mode_PWM, PCA_Mode_Capture, PCA_Mode_SoftTimer, PCA_Mode_HighPulseOutput

PCA_InitStructure.PCA_PWM_Wide = PCA_PWM_8bit; //PCA_PWM_8bit, PCA_PWM_7bit, PCA_PWM_6bit

PCA_InitStructure.PCA_Interrupt_Mode = DISABLE; //PCA_Rise_Active, PCA_Fall_Active, ENABLE, DISABLE

PCA_InitStructure.PCA_Value = (u16)((1 << 8) * (1 - 0.5)); //For software timing, it is the match comparison value

PCA_Init(PCA0,&PCA_InitStructure);

PCA_InitStructure.PCA_Mode     = PCA_Mode_PWM; //PCA_Mode_PWM, PCA_Mode_Capture, PCA_Mode_SoftTimer, PCA_Mode_HighPulseOutput

PCA_InitStructure.PCA_PWM_Wide = PCA_PWM_7bit; //PCA_PWM_8bit, PCA_PWM_7bit, PCA_PWM_6bit

PCA_InitStructure.PCA_Interrupt_Mode = DISABLE; //PCA_Rise_Active, PCA_Fall_Active, ENABLE, DISABLE

PCA_InitStructure.PCA_Value = (u16)((1 << 7) * (1 - 0.5)); //For software timing, it is the match comparison value

PCA_Init(PCA1,&PCA_InitStructure);

PCA_InitStructure.PCA_Clock    = PCA_Clock_1T; //PCA_Clock_1T, PCA_Clock_2T, PCA_Clock_4T, PCA_Clock_6T, PCA_Clock_8T, PCA_Clock_12T, PCA_Clock_Timer0_OF, PCA_Clock_ECI

PCA_InitStructure.PCA_IoUse    = PCA_P24_P25_P26_P27;//PCA_P12_P11_P10_P37, PCA_P34_P35_P36_P37, PCA_P24_P25_P26_P27

PCA_InitStructure.PCA_Interrupt_Mode = DISABLE; //ENABLE, DISABLE

PCA_InitStructure.PCA_Polity = PolityHigh; //Priority setting PolityHigh, PolityLow

PCA_Init(PCA_Counter,&PCA_InitStructure);

}

void main(void)

{

GPIO_config();

PCA_config();

UpdatePwm(PCA0, (1 << 8) * (1 - 0.75));

UpdatePwm(PCA1, (1 << 7) * (1 - 0.25));

while(1)

{

}

}

Experimental phenomena

16-bit software timer mode to generate PWM signal

PWM frequency = PCA clock frequency / PWMx_DUTY

Modify PWMx_DUTY in PCA.h

Modify the corresponding pin in PCA_Handler

//========================================================================

// 函数: void PCA_Handler (void) interrupt PCA_VECTOR

// Description: PCA interrupt handler.

// Parameters: None

// Returns: none.

// Version: V1.0, 2012-11-22

//========================================================================

void PCA_Handler (void) interrupt PCA_VECTOR

{

if(CCF0) //PCA module 0 interrupt

{

CCF0 = 0; // Clear PCA module 0 interrupt flag

if(P25) CCAP0_tmp += PCA_Timer0; //output is high level, then load the high level time length to the mapping register

else CCAP0_tmp += PWM0_low; //If the output is low level, load the low level time length into the mapping register

CCAP0L = (u8)CCAP0_tmp; //Write the mapping register into the capture register, write CCAP0L first

CCAP0H = (u8)(CCAP0_tmp >> 8); // write CCAP0H later

}

if(CCF1) //PCA module 1 interrupt

{

CCF1 = 0; // Clear PCA module 1 interrupt flag

if(P26) CCAP1_tmp += PCA_Timer1; //output is high level, then load the high level time length to the mapping register

else CCAP1_tmp += PWM1_low; //If the output is low level, load the low level time length into the mapping register

CCAP1L = (u8)CCAP1_tmp; //Write the mapping register into the capture register, write CCAP0L first

CCAP1H = (u8)(CCAP1_tmp >> 8); //后写CCAP0H

}

if(CCF2) //PCA module 2 interrupt

{

CCF2 = 0; // Clear PCA module 1 interrupt flag

if(P27) CCAP2_tmp += PCA_Timer2; //output is high level, then load the high level time length into the mapping register

else CCAP2_tmp += PWM2_low; //If the output is low level, load the low level time length into the mapping register

CCAP2L = (u8)CCAP2_tmp; //Write the mapping register into the capture register, write CCAP0L first

CCAP2H = (u8)(CCAP2_tmp >> 8); // write CCAP0H later

}

if(CF) //PCA overflow interrupt

{

CF = 0; // Clear PCA overflow interrupt flag

}

}

main.c

#include "./Drivers/config.h"

#include "./Drivers/delay.h"

#include "./Drivers/GPIO.h"

#include "./Drivers/PCA.h"

void GPIO_config(void)

{

GPIO_InitTypeDef GPIO_InitStructure; //Structure definition

GPIO_InitStructure.Mode = GPIO_OUT_PP; //Specify IO input or output mode, GPIO_PullUp, GPIO_HighZ, GPIO_OUT_OD, GPIO_OUT_PP

GPIO_InitStructure.Pin = GPIO_Pin_5 | GPIO_Pin_6; //Specify the IO to be initialized, or operation

GPIO_Inilize(GPIO_P2, &GPIO_InitStructure); //P2.5 and P2.6 are initialized as push-pull output

}

void PCA_config(void)

{

PCA_InitTypeDef PCA_InitStructure;

PCA_InitStructure.PCA_Mode     = PCA_Mode_HighPulseOutput; //PCA_Mode_PWM, PCA_Mode_Capture, PCA_Mode_SoftTimer, PCA_Mode_HighPulseOutput

PCA_InitStructure.PCA_PWM_Wide = 0; //PCA_PWM_8bit, PCA_PWM_7bit, PCA_PWM_6bit

PCA_InitStructure.PCA_Interrupt_Mode = ENABLE; //PCA_Rise_Active, PCA_Fall_Active, ENABLE, DISABLE

PCA_InitStructure.PCA_Value = 65535; //For software timing, it is the match comparison value

PCA_Init(PCA0,&PCA_InitStructure);

PCA_InitStructure.PCA_Mode     = PCA_Mode_HighPulseOutput; //PCA_Mode_PWM, PCA_Mode_Capture, PCA_Mode_SoftTimer, PCA_Mode_HighPulseOutput

PCA_InitStructure.PCA_PWM_Wide = 0; //PCA_PWM_8bit, PCA_PWM_7bit, PCA_PWM_6bit

PCA_InitStructure.PCA_Interrupt_Mode = ENABLE; //PCA_Rise_Active, PCA_Fall_Active, ENABLE, DISABLE

PCA_InitStructure.PCA_Value = 65535; //For software timing, it is the match comparison value

PCA_Init(PCA1,&PCA_InitStructure);

PCA_InitStructure.PCA_Clock    = PCA_Clock_12T; //PCA_Clock_1T, PCA_Clock_2T, PCA_Clock_4T, PCA_Clock_6T, PCA_Clock_8T, PCA_Clock_12T, PCA_Clock_Timer0_OF, PCA_Clock_ECI

PCA_InitStructure.PCA_IoUse    = PCA_P24_P25_P26_P27; //PCA_P12_P11_P10_P37, PCA_P34_P35_P36_P37, PCA_P24_P25_P26_P27

PCA_InitStructure.PCA_Interrupt_Mode = DISABLE; //ENABLE, DISABLE

PCA_InitStructure.PCA_Polity = PolityHigh; //Priority setting PolityHigh, PolityLow

PCA_Init(PCA_Counter, &PCA_InitStructure);

}

void main(void)

{

GPIO_config();

PCA_config();

PWMn_Update(PCA0, (u16)(PWM0_DUTY * 0.75));

PWMn_Update(PCA1, (u16)(PWM1_DUTY * 0.25));

EA = 1;

while(1)

{

}

}

Experimental phenomena

Capture mode measures cycle length

Modify PCA_Handler in PCA.c

//========================================================================

// 函数: void PCA_Handler (void) interrupt PCA_VECTOR

// Description: PCA interrupt handler.

// Parameters: None

// Returns: none.

// Version: V1.0, 2012-11-22

//========================================================================

void PCA_Handler (void) interrupt PCA_VECTOR