1. PULSE WIDITH MODULATION EE 587 Presented by Viswanadha Kakarlapudi

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

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

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

5. Implementing PWM Using PCA 8-Bit PWM

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

7. 16-Bit PWM Using the PCA

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

9. 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

10. 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

11. 16-Bit PWM Using an On-Chip Timer

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

13. How Servos Work

14. References  www.cygnal.com/appnotes www.cygnal.com/appnotes  www.brookshiresoftware.com www.brookshiresoftware.com