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Digital system design Digital Systems Digital vs Analog Waveforms +5 +5 1 V V Time –5 Digital: only assumes discrete values Time –5 Analog: values vary over a broad range continuously Digital signal status Wave form Decimal base 10 Binary base Hexadecimal base 16 From decimal to binary Surplus Surplus Surplus Surplus Decimal to hexadecimal Surplus Surplus Surplus Binary to Hexadecimal Hexadecimal to Binary  Design Loop for Digital Hardware  The basic design loop:  Initial design takes creativity and experience  CAD tools are used for simulation and to work out details  The Entire Development Process  Design is only one part  Verification and testing are also important – this is called design verification  Errors may not be uncovered until after the prototype is made  Errors may not be uncovered until after “release”!  Pentium bug  Simulation Phase  Functional simulation   Timing simulation    Test the circuit to determine if it correctly performs all the functions that are required Test the circuit to determine if it meets the timing requirements Correct functionality does not necessarily lead to fast speed The physical design / layout will affect the timing   Inherent gate delays Physical wiring leaves metal traces that have resistance  CAD Tools  There are a number of commonly used industry standard CAD tools    CAD = Computer Aided Design Altera, Cadence, Mentor Graphics, Synopsys, Synplicity, Xilinx Tools are used for multiple purposes   Synthesis, timing simulation, functional simulation, layout Can even download the design onto a PCB Analog Signal Continuous—represented analogously as a value of a continuously variable parameter i) position of a needle on a meter ii) rotational angle of a gear iii) amount of water in a vessel iv) electric charge on a capacitor Analog-to-Digital Conversion Terminology analog-to-digital converter: ADC, A/D, A2D; converts an analog signal to a digital signal digital-to-analog converter: DAC, D/A, D2A An embedded system’s surroundings typically involve many analog signals Resolution Let n = Vmax 3=11 M = 2n steps on the digital scale d0 = = 0b00 dVmax - r = = 0b11 (no dVmax ) 2=10 r, resolution: smallest 1=01 analog change resulting from changing one bit 0V 0=00 ADC using successive approximation   Given an analog input signal whose voltage should range from to 15 volts, and an 8-bit digital encoding, calculate the correct encoding for volts Then trace the successive-approximation approach to find the correct encoding Assume M = 2n – a / Vmax = d / M / 15 = d / (256 - 1) d = 85 or binary 01010101 ADC Converter 5V ADC converter using reference source Digital To Analog (DAC)