PULSE WIDITH MODULATION EE 587 Presented by Viswanadha Kakarlapudi

Overview  Introduction  Implementing 16-Bit PWM Using the PCA  16-Bit PWM Using the On-Chip Timer  How Servos Work  References

Introduction  Signal Information is encoded in the duty cycle  Input to the PWM implementation is an integer proportional to the duty cycle desired

Implementing PWM Using PCA Introduction to PCA (Programmable Counter Array)

Implementing PWM Using PCA 8-Bit PWM

 Duty cycle can be changed by single 8-bit write to PCAOCPHn

16-Bit PWM Using the PCA

 Duty cycle can be changed by single 16-bit write to the variable PWM

16-Bit PWM Using an On-Chip Timer  The C8051F2xx family SoC’s feature three on- board timers that can be used for PWM generation  The C8051F226-TB features a low-pass filter that can be readily used for the PWM DAC

16-Bit PWM Using an On-Chip Timer  Timer is set to the amount of time the PWM wave is high during one cycle  When the timer overflows, the program vectors to an ISR to take a port pin high or low to produce the PWM wave  The smallest pulse width that can be assigned is 19 clock cycles. The ISR takes 14 cycles to take the PWM wave from high to low

16-Bit PWM Using an On-Chip Timer

How Servos Work  Servos are commanded through PWM signals  In order for the Servo to hold position, the command must be sent every 20ms

How Servos Work

References  