Generate Quadrature Signals with PIC16F1575


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    Default Generate Quadrature Signals with PIC16F1575

    I had a requirement to generate two 100 KHz, 50% duty cycle signals that differed in phase by 90 degrees. Based on experience with the PIC16F1575, the solution involved using the MCU's PWM modules with its internal RC oscillator configured to operate at 32 MHz.

    A PWM frequency of 100 KHz corresponds to a period of 10 uSec and per the MCU datasheet we have:

    PWM Period = [(PWMxPR +1) * Prescale)] / (PWMxCLK)

    With a PWM period of 10 uSec, Prescale = 1 and PWMxCLK = 32 MHz, then 16-bit register PWMxPR must contain $0140 or 320 decimal.

    To achieve a PWM 50% duty cycle, 16-bit register 16-bit register PWMxDC must contain half of the Period register or 160 decimal. And, to achieve a 2.5 uSec PWM1 vs PWM2 offset, 16-bit register PWM1DC must contain 80 decimal.

    Based on the attached program, the following performance was noted.

    Frequency: PWM1 = PWM2 = 99.75 KHz

    Duty Cycle: PWM1 = PWM2 = 50% +/- 0.4%

    Phase Shift: PWM1 leads PWM2 by 2.5 microseconds
    Attached Thumbnails Attached Thumbnails Required_Quadrature_Output_1.jpg‎   Scope_Screenshot.jpg‎  
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