BAI_007_VXL_PIC_PWM

7/22/2019 BAI_007_VXL_PIC_PWM

1/8

BI7

GII THIU KHO ST PWM

S KHI PWM TNH CHU K XUNG PWM TNH H S CHU K PWM

TP LNH C CHO PWM LNH NH CU HNH KHI CCP LNH THIT LP H S CHU K LNH SETUP_TIMER_2 - LNH NH CU HNH CHO TIMER_2 LNH SET_TIMERx(value) - LNH THIT LP GI TR BT U CHO TIMER

CC CHNG TRNH NG DNG PWM


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ai hoc s pham ky thuat tp HCM Khoa ien ien t Nguyen nh Phu

86 Bai 7: PWM cua PIC va lap trnh C.

I. GII THIUVi iu khinPIC h 16F877A c 2b PWM dng iu khin tc ng c DC.

Phn ny s kho st chi tit khi PWM ca PIC v tp lnh lp trnh C cho PWM.

II. KHO ST PWM1. S KHI PWM

PWM ca PIC16F877A c s khi nh hnh 7-1:

Hnh7-1:

S khi caPWM PIC 16F877A.

Khi PWM gm c 2 mch so snh: mch so snh 8 bit vi mch sosnh 10 bit.

Mch so snh 8 bit s so snh gi tr m ca timer2 vi gi tr ca thanh ghi PR2 (period register),gi tr trong timer2 tng t gi tr t trc cho n khi bng gi tr ca PR2 th mch so snh s set flip flopRS lm ng ra CCPx ln mc1. ng thi np gi tr 10 bit t thanh ghi CCPRxL sang thanh ghi CCPRxH,timer2 b reset v bt u m li cho n khi gi tr ca timer2 bng gi tr ca CCPRxH th mch so snhs reset flip flop RS lm ng ra CCPx v mc 0. Qu trnh ny lp li.

Dng sng iu ch PWM nh hnh 7-2:

Hnh 7-1:Dng sng PWM.

Chu k khng thay i, mun thay i thi gian xung mc 1 th ta thay i h s chu k (dutycycle). Khi h s chu k thay i th in p hay dng trung bnh thay i.

H s chu k cng ln th dng trung bnh cng ln, nu iu khin ng c s lm thay i tc .


3/8


Bai 7: PWM cua PIC va lap trnh C. 87

2. TNH CHU K XUNG PWMChu k PWM ca PIC16F877A c tnh theo cng thc:

2**4*]1)2[( TMROSCPWM PVTPRPERIOD

Trong :OSCT l chu k ca t thch anh to dao ng

2TMRPV (prescale value) gi tr chia trc ca timer2

Khi gi tr ca timer 2 (TMR2) bng gi tr ca thanh ghi PR2 th 3 s kin theo sau s xy ra:

Thanh ghi TMR2 bxa Tn hiu ng ra CCPx ln mc 1, ngoi tr h s chu k bng 0% th CCPx vn mc 0. H s chu kPWM c chuyn t thanh ghi CCPRxL sang thanh ghi CCPRxH.

3. TNH H S CHU K XUNG PWMH s chu k c thit lp bi gi tr lu trong thanh ghi 10 bit gm CCPRxL 8 bit v 2 bit cn li l

bit th 4 v th 5 trong thanh ghi CCPxCONk hiu l CCPxCON.Gi tr ca h s chu k l 10 bit nn c th thay i t 0 n 1023 to ra 1024 cp gi tr iu khin.

Gi tr 10 bit th 8 bit c trng s ln lu trong thanh ghi CCPRxL v 2 bit cn li c trng s thp th CCPxCON.

H s chu k ca PIC16F877A c tnh theo cng thc:

2**)4:5:(_ TMROSCPWM PVTCCPxCONCCPRxLCYCLEDUTY

III. CC LNH IU KHIN1. LNH NH CU HNH KHI CCP

C php: setup_ccp1 (mode) or setup_ccp1 (mode, pwm)

Thng s : model h ng s . Gi tr ca mode xem trong file thi t b, mt vi thng s :Disable the CCP: CCP_OFFSet CCP to PWM mode: CCP_PWM Enable Pulse Width Modulator

Chc nng: Khi to khi CCP.

Hiu lc: Cho t t c cc vi i u khi n PIC tch hp ph n cng CCP

V d: setup_ccp1(CCP_PWM); khi to khi CCP1 c chc nng PWM

2. LNH THIT LP H S CHU KC php: set_pwm1_duty (value)

Thng s: valuec th l hng s 8 bit hoc 16 bit.

Chc

nng:

Ghi gi tr 10 bit vo PWM thit lp h s chu k.

Gi tr 10 bit c dng xc nh lng thi gian ca tn hiu PWM mc 1 trong mt chuk nh sau


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value*(TOSC)*t2divTrong t2div l gi tr chia trc ca timer2 c thit lp lnh setup_timer2.

V d: // cho tn s t thch anh l 20MHz, 1.2 khz frequency,// gi tr chi trc ca timer2 l t2div =16// the following sets the duty to 50% (or 416 us).

long duty;

duty = 512; // .000416/(16*(1/20000000))

set_pwm1_duty(duty);

3. LNH SETUP_TIMER_2 - LNH NH CU HNH CHO TIMER_2C php: setup_timer_2(mode, period, postscale)

Thng s: mode c th l 1 trong cc thng s: T2_DISABLED, T2_DIV_BY_1, T2_DIV_BY_4,T2_DIV_BY_16

Periodl s nguyn c gi tr t 0 n 255 dng xc nh khi no gi tr timerb reset.

postscalel s nguyn c gi tr t1 n 16 dng xc nh timer trn bao nhiu ln trckhi pht sinh tn hiu ngt.

Chc nng: khi to cho TIMER2.

Mode ch nh kiu b chia ca timer t tn s ca mch dao ng.

Gi tr ca timer c th c hoc ghi dng lnh GET_TIMER2() v SET_TIMER2().

TIMER2 l timer 8 bit.

C hiu lc: cho tt c cc vi iu khin PIC c timer 2.

V d: SETUP_TIMER_2 (T1_ DIV_BY_4,0XC0,2);

S dng thch anh 20MHz, qua b chia 4 cn 5MHz, chu k l 200ns. Vi lnh khi to ny th timer2 s tng gi tr sau 4 chu k xung 200ns (tng ng800ns), s trn sau mi khong thi gian 153.6s v pht sinh yucu ngt sau 307.3 s.

4. LNH SET_TIMERx(value) - LNH THIT LP GI TR BT U CHO TIMERC php: set_timerX(value) ; x l 0, 1, 2

Thng s: valuel hng s nguyn 8 hoc 16 bit dng thit lp gi tr mi cho timer.

Chc nng: thit lp gi tr bt u cho TIMER.

C hiu lc: cho tt c cc vi iu khin PIC c timer.

V d: SET_TIMER2 (0); //reset timer2

IV. NG DNG PWM1. YU CU IU KHIN

S dng PWM ca PIC16F877A iu khin tc ng c 10 cp.Cho tn s t thch anh l10MHz. Cho chu k PWM l 1ms. Hy tnh ton cc thng s iu khin ng c.

Tnh ton:

Tn s thch anh: MHzfOSC 10 nn chu k l: nsSMHzF

T

OSC

OSC 1001,010

11

Chu k PWM: nsmSPVTPRPERIOD TMROSCPWM 000,000,11**4*]1)2[( 2


5/8



Ch bit c nsTOSC

100 cn cc thng s 2,2 TMRPVPR th cha bit.

Phi chn 1 thng s v tnh thng s cn li: ch 2PR c gi tr 8 bit t 0 n 255, cn2TMR

PV c3 gi tr l chia 1, chia 4 v chia 16.

Chn h s chia ln nht l 16 hay 162

TMRPV

Khi tm gi tr cn li 2PR :

15616*100*4

000,000,1

**4]1)2[(

2

ns

ns

PVT

PERIODPR

TMROSC

PWM

Vy 1552 PR .Lnh khi to cho timer2 l: setup_timer_2(T2_DIV_BY_16, 155, 1)

Tnh h s chu k:

H s chu k thay i s lm gi tr trung bnh ca tn hiu thay i, h s chu k nh nht l bng 0khi tn hiu ra CCPx mc 0, h s chu k tng lm tn hiu xut hin v gi tr trung bnh tng, h schu k ln nht bng chu k ca PWM.

Cho h s chu k bng chu k tnh ton gii hn h s chu k:

MAXPWMPWMPERIODCYCLEDUTY

_

_

Ta c cng thc: 2**)4:5:(_ TMROSCPWM PVTCCPxCONCCPRxLCYCLEDUTY

Ta tm gi tr ln nht ca 4:5:CCPxCONCCPRxL .

Suy ra:22

_

**

_)4:5:(

TMROSC

PWM

TMROSC

MAXPWM

PVT

PERIOD

PVT

CYCLEDUTYCCPxCONCCPRxL

62516*100

000,000,1

*)4:5:(

2

ns

ns

PVT

PERIODCCPxCONCCPRxL

TMROSC

PWM

PWM c phn gii l 10 bit tng ng vi h s chu k thay i t 0 n 1023, nhng vi yu cuny th h s chu k thay i t 0 n gi tr ln nht l 625.

Vi gi tr ny ta thit lp s cp iu khin tc ng c, chn s cp l 10, thay i s cp bng 2nt nhn Tng v Gim. Ch khng tnh cp 0.

Gi tr thay i cho mi cp l 62,5 lm trn l 62.

Chng trnh c 4 nt nhn: START, STOP, UP, DW.

Khi nhn UP th tng gi tr tng h s chu k, khi nhn DW th gim h s chu k, c kim tragii hn tng v gim, c kim tra ng c ang hot ng hay khng, nu ng c khng hot ng th chtng gi tr h s chu k, nu ng c ang chy th cp nht gi tr thay i, da vo bit tt bit trng thing c.

Khi nhn START th ng c chy, khi nhn STOP th ng c ngng.


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#include

#fuses NOWDT,PUT,HS,NOPROTECT,NOLVP

#use delay(clock=10000000)

#define START PIN_A0

#define STOP PIN_A1

#define UP PIN_A2

#define DW PIN_A3

int16 bientocdo=0;

int1 tt;

void main()

{

set_tris_A(0x07f);

setup_ccp1(CCP_PWM);

setup_timer_2(T2_div_by_16,155,1);

bientocdo=0; //xoa bien toc do

set_pwm1_duty(bientocdo); //DUTY=0, CAP THU 0 DE TAT DONG CO

tt=0;

while(1)

{

if (!input(UP)) //NHAN PHIM TANG TOC

{ delay_ms(100);

if (bientocdo < 620)

{ bientocdo= bientocdo+62;

If (tt==1)

{ set_pwm1_duty(bientocdo); }

}

}

if (!input(DW)) //NHAN PHIM GIAM TOC


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{ delay_ms(100);

if (bientocdo > 0)

{bientocdo= bientocdo - 62;

If (tt==1)

{ set_pwm1_duty(bientocdo); }

}

}

if (!input(START)) //NEU NHAN PHIM START

{

set_pwm1_duty(bientocdo); //cho dco chay thuan

tt=1;

}

if (!input(STOP)) // NEU NHAN PHIM STOP

{

bientocdo=0; tt=0;

set_pwm1_duty(bientocdo); //DUNG DONG CO

}

}

}

B[I 6-1: IU KHIN NG C CHY VI TC CP 1, CHU K 1MS, H S CHU K 62, TNS THCH ANH 10MHZ.

#include

#fuses NOWDT,PUT,HS,NOPROTECT,NOLVP


void main()

{



set_pwm1_duty(62);

}

B[I 6-2: IU KHIN NG C CHY VI TC CP 2, CHU K 1MS, H S CHU K 124, TNS THCH ANH 10MHZ.

#include #fuses NOWDT,PUT,HS,NOPROTECT,NOLVP


void main()

{



set_pwm1_duty(124);

}

TT 4:51:1 CONCCPLCCPR DCPWM _ PPWM_ CAP O


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92 Bai 7: PWM cua PIC va lap trnh C

1 0 0 S 819S 0%2 10 8 S 819S 1%3 10+10 16 S 819S 2%4 20+10 24 S 819S 3%

1023 819S 819S 100%

0

1

2

3

4

5

6

7

1ms

10ms

Documents

BAI_007_VXL_PIC_PWM