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Presentation: ADC – Analog to Digital Converter and PWM Waveform Generation with EZDSP2812 Professor: Chen, Pei-Chung 陳沛仲 Student: Thanh-Nhan Nguyen 阮誠仁 2008, December, 11th 1 1. ADC module introduction 2. PWM waveform generation 3. An example 2 ADC – Analog to Digital Converter EZDSP 2812 ADC module consists of a 12-bit ADC. Functions of the ADC module include: • 12-bit ADC core with built-in S/H • Analog input: 0.0 V to 3.0 V (Voltages above 3.0 V produce full-scale conversion result5s.) • Fast conversion rate: 80 ns at 25-MHz ADC clock, 12.5 MSPS • 16-channel, MUXed inputs • Sixteen result registers (individually addressable) to store conversion values − The digital value of the input analog voltage is derived by: Digital Value = 0 Digital Value = 4096 * ((Input Analog Voltage- ADCLO)/3) Digital Value = 4095 When input <= 0V When 0V < input <3V When input >=3V ADC voltage resolution is: (0V - 3V) / 4096 codes = 3V / 4096 codes ~ 0.000732 volts/code ~ 0.732 mV/code 3 Fig 1. ADC pin connections with internal reference 4 Initialize System Control Initialize GPIO Clear all interrupts and initialize PIE vector table Initialize all the Device Peripherals Specific code for A/D conversion Fig 2. The procedure to use ADC – Analog to Digital Converter 5 Characteristics of the PWMs are as follows: • 16-bit registers • Wide range of programmable deadband for the PWM output pairs • Change of the PWM carrier frequency for PWM frequency wobbling as needed • Change of the PWM pulse widths within and after each PWM period as needed • External-maskable power and drive-protection interrupts • Pulse-pattern-generator circuit, for programmable generation of asymmetric, symmetric, and four-space vector PWM waveforms • Minimized CPU overhead using auto-reload of the compare and period registers • The PWM pins are driven to a high-impedance state when the PDPINTx pin is driven low and after 6 EVA EVB Fig 3. The procedure to generate the PWM waveform 7 Initialize System Control Initialize GPIO Clear all interrupts and initialize PIE vector table Initialize all the Device Peripherals Specific code for PWM waveform generation Fig 4. The procedure to generate the PWM waveform 8 Get the analog signal from ADCINA0 (P9) A/D conversion Using Digital signal to change the duty cycle of PWM waveform generation Output PWM waveform to P8 Processing… Input Analog Voltage 3V AD conversion Digital Value For PWM waveform Output Fig 5. The steps for A/D conversion and PWM waveform generation 9 Osciloscope Display +5V R 1K DSP power source Var-R 10K 2812 CPU Zener 3V ADC GND PWM PWM1 (P8) ADCLO (P9) Fig 6. The connections for ADC and PWM generation 10 Thank you very much for your listening! 11