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aLec28_DAC - Introduction to Embedded Microcomputer Systems...

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Introduction to Embedded Microcomputer Systems Lecture 28.1 Jonathan W. Valvano Recap Synchronization: hardware/software, between threads SCI interrupts Fifo queue: what why how Overview Design a DAC Experimental method Output a sine wave Digital to Analog Conversion Signal generation (sound, image, touch…) Output to affect external devices (power, flow, heat…) The DAC precision is the number of distinguishable DAC outputs (e.g., 16 alternatives, 4 bits). The DAC range is the maximum and minimum DAC output (0 to 5V). The DAC resolution is the smallest distinguishable change in output. (5V/16 =0.31V) Range(volts) = Precision(alternatives) • Resolution(volts) The DAC accuracy is (Actual - Ideal) / Ideal For example, if we were to build a 2-bit DAC. Assume V OH of the 9S12 is 5, and its V OL is 0 N Q 1 Q 0 V 1 (V) V 2 (V) 0 0 0 0.00 0.00 1 0 5 1.25 1.67 2 5 0 2.50 3.33 3 5 5 3.75 5.00 Q 1 Q 0 10k Ω 20k Ω V 1 20k Ω Q 1 Q 0 10k Ω 20k Ω V 2 6812 bit3 bit2 bit1 bit0 static testing V out voltmeter I out speaker 6812 bit3 bit2 bit1 bit0 dynamic testing Figure 8.1. DAC allows the software to create music.
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