PWM IMPLEMENTATION

WHAT IS PWM?

PWM (PULSE WIDTH MODULATION)

TIMERS

TIMER BLOCK DIAGRAM

TIMER OPERATION

1. ONE SHOT 2. CONTINUOUS MODE 3. COUNTER MODE 4. COMPARATOR COUNTER MODE 5. PWM MODE 6. CAPTURE MODE 7. COMPARE MODE 8. GATED MODE

PWM SYSTEM

THE TIMER OUTPUTS A PWM SIGNAL THROUGH

A GPIO PORT PIN THE TIMER INPUT IS THE SYSTEM CLOCK (18.432 MHz)

PWM ALGORITHM 1. THE TIMER COUNTS UP TO THE 16-BIT PWM

HIGH AND LOW BYTE REGISTERS. (TxPWMH,TxPWML) 2. WHEN THE TIMER COUNT VALUE MATCHES

THE PWM VALUE, THE TIMER OUTPUT TOGGLES.

3. THE TIMER CONTINUES COUNTING UNTIL IT REACHES THE RELOAD VALUE STORED IN THE TIMER RELOAD HIGH AND LOW BYTE REGISTERS

PWM ALGORITHM 4. UPON REACHING THE RELOAD VALUE, THE

TIMER GENERATES AN INTERRUPT;THE COUNT VALUE IN THE TIMER HIGH AND LOW BYTE REGISTERS IS RESET TO 0001H AND COUNTING RESUMES.

5. SET THE TIMER I/O POLARITY (TPOL) REGISTER ENTRY.

0 TIMER OUTPUT SIGNAL BEGIN AS low 1 - TIMER OUTPUT SIGNAL BEGIN AS high

PWM CONFIGURATION

PWM CONFIGURATION

PWM COMPUTATION

BASIC TIMER OPERATION

count = 1; while (count

PRESCALE SYSTEM

Z8 encore clock - 18.432 MHz 16 bit counter Problem??? they are not enough to produce significant

delay values. Solution!!! Prescaling to slow down the timer clock to

generate longer delays

PRESCALING COMPUTATION

Setting the prescaler to divide by N = 64; 18.432 MHz/64 = 288 kHz NOTE: prescaler can be set to divide by powers

of 2 from 20 = 1 to 27 = 128

TIMER 0-3 CONTROL 1 REGISTER (TxCTL1)

TIMER MODE/OPERATION

TIMER INITIALIZATION

1. Disable the timer 2. Set the mode, prescaler value, and timer

polarity 3. Set the counter start value 4. Set the reload value 5. Setup or disable timer interrupt and ISR 6. Enable timer

SAMPLE CODE FOR PWM

REQUIREMENT: Generate a 1-kHz PWM signal with a

50% duty cycle at the PC1 pin.

GIVEN PARAMETERS

1. TIMER 1 configured in PWM mode 2. Reload period of 1ms (freq = 1khz) 3. DUTY CYCLE = 50%

#include #define RELOAD_VALUE 18432 //PWM period (sec.) = (RELOAD x Prescaler)/system //clock (Hz) #define PWM_VALUE 9216

#define TMODE 0x03 //Timer mode is PWM mode

#define PRESCALER 0x00 //prescaler = 1

DI(); T1CTL &= ~0x80; //Disable Timer 1 T1CTL |= (0x00

T1H = 0x00; //initial value is 1 T1L = 0x01; T1PWMH = (PWM_VALUE >> 8); T1PWML = (PWM_VALUE & ~0xFF00); //PWM_VALUE loaded, set duty cycle

T1RH = (RELOAD_VALUE >> 8); T1RL = (RELOAD_VALUE & ~0xFF00);

//RELOAD_VALUE loaded, set PWM period

IRQ0ENH &= ~0x40; IRQ0ENL &= ~0x40; //Timer 1 interrupt

disabled

PCDD |= 0x02; //PCI/T1OUT pin is output PCAF |= 0x02; //turn on alternate function of PC1, T1CTL |= 0x80; //Enable Timer1 //After the previous line of code, PWM will

automatically start. //PWM period is 1 kHz, with 50% duty

cycle EI();

PWM IMPLEMENTATIONWHAT IS PWM?TIMERSTIMER BLOCK DIAGRAMTIMER OPERATIONPWM SYSTEMPWM ALGORITHMPWM ALGORITHMPWM CONFIGURATIONPWM CONFIGURATIONPWM COMPUTATIONSlide Number 12Slide Number 13BASIC TIMER OPERATIONPRESCALE SYSTEMPRESCALING COMPUTATIONTIMER 0-3 CONTROL 1 REGISTER(TxCTL1)Slide Number 18Slide Number 19Slide Number 20TIMER MODE/OPERATIONSlide Number 22TIMER INITIALIZATIONSAMPLE CODE FOR PWMGIVEN PARAMETERSSlide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31