【導(dǎo)讀】本文介紹了一種基于FPGA芯片上實(shí)現(xiàn)出租車計(jì)價(jià)器功能的設(shè)計(jì)方法，主要闡述如何使用新興的EDA器件取代傳統(tǒng)的電子設(shè)計(jì)方法，不僅實(shí)現(xiàn)了出租車計(jì)價(jià)器所需的一些基本功能，同時(shí)考慮到出租車行業(yè)的一些特殊性，更注重了把一些新的思路加入到設(shè)計(jì)中。本設(shè)計(jì)主要借助了FPGA芯片，使用VerilogHDL語言靈活編程來實(shí)現(xiàn)多方面的計(jì)費(fèi)，這樣不僅使其不拘泥于硬件，具有更強(qiáng)的移植性，而且增強(qiáng)了實(shí)用價(jià)值，更加利于產(chǎn)品升級(jí)。本設(shè)計(jì)參考成都的出租車計(jì)費(fèi)標(biāo)準(zhǔn)，利用VerilogHDL語言設(shè)計(jì)出租車計(jì)價(jià)器，主要具有行駛路程動(dòng)態(tài)顯示計(jì)費(fèi)，等待累計(jì)時(shí)間計(jì)費(fèi)及最后的總費(fèi)用動(dòng)態(tài)顯示功能，突出了其作為硬件描述語言的良好的可讀性、可移植性和易理解等優(yōu)點(diǎn)。依據(jù)國家有關(guān)法律、法規(guī)，出租車計(jì)價(jià)器是列入國家首批強(qiáng)制檢定的工作計(jì)量器具之一，也是近年來國家質(zhì)量技術(shù)監(jiān)督部門強(qiáng)化管理的六類重點(diǎn)計(jì)量器具之一。傳統(tǒng)的出租車計(jì)價(jià)器由于發(fā)展使用了十幾年，在穩(wěn)定性、成本、以及使用習(xí)慣上都具有一些優(yōu)勢(shì)。

　　

【正文】 application is not affected when additional processing is added.Top Five Benefits of FPGA TechnologyPerformance– Taking advantage of hardware parallelism, FPGAs exceed the puting power of digital signal processors (DSPs) by breaking the paradigm of sequential execution and acplishing more per clock cycle. BDTI, a noted analyst and benchmarking firm, released benchmarks showing how FPGAs can deliver many times the processing power per dollar of a DSP solution in some Controlling inputs and outputs (I/O) at the hardware level provides faster response times and specialized functionality to closely match application requirements.Time to market– FPGA technology offers flexibility and rapid prototyping capabilities in the face of increased timetomarket concerns. You can test an idea or concept and verify it in hardware without going through the long fabrication process of custom ASIC You can then implement incremental changes and iterate on an FPGA design within hours instead of weeks. Commercial offtheshelf (COTS) hardware is also available with different types of I/O already connected to a userprogrammable FPGA chip. The growing availability of highlevel software tools decrease the learning curve with layers of abstraction and often include valuable IP cores (prebuilt functions) for advanced control and signal processing.Cost– The nonrecurring engineering (NRE) expense of custom ASIC design far exceeds that of FPGAbased hardware solutions. The large initial investment in ASICs is easy to justify for OEMs shipping thousands of chips per year, but many end users need custom hardware functionality for the tens to hundreds of systems in development. The very nature of programmable silicon means that there is no cost for fabrication or long lead times for assembly. As system requirements often change over time, the cost of making incremental changes to FPGA designs are quite negligible when pared to the large expense of respinning an ASIC.Reliability– While software tools provide the programming environment, FPGA circuitry is truly a “hard” implementation of program execution. Processorbased systems often involve several layers of abstraction to help schedule tasks and share resources among multiple processes. The driver layer controls hardware resources and the operating system manages memory and processor bandwidth. For any given processor core, only one instruction can execute at a time, and processorbased systems are continually at risk of timecritical tasks preempting one another. FPGAs, which do not use operating systems, minimize reliability concerns with true parallel execution and deterministic hardware dedicated to every task.Longterm maintenance– As mentioned earlier, FPGA chips are fieldupgradable and do not require the time and expense involved with ASIC redesign. Digital munication protocols, for example, have specifications that can change over time, and ASICbased interfaces may cause maintenance and forward patibility challenges. Being reconfigurable, FPGA chips are able to keep up with future modifications that might be necessary. As a product or system matures, you can make functional enhancements without spending time redesigning hardware or modifying the board layout. Introduction to signal generatorOverviewA signal generator, also known variously as a test signal generator, function generator, tone generator, arbitrary waveform generator, digital pattern generator or frequency generator is an electronic device that generates repeating or nonrepeating electronic signals (in either the analog or digital domains). They are generally used in designing, testing, troubleshooting, and repairing electronic or electroacoustic devices.There are many different types of signal generators, with different purposes and applications (and at varying levels of expense)。 in general, no device is suitable for all possible applications.Traditionally, signal generators have been embedded hardware units, but since the age of multimediaPCs, flexible, programmable software tone generators have also been available.Function generatorsA function generator is a device which produces simple repetitive waveforms. Such devices contain an electronic oscillator, a circuit that is capable of creating a repetitive waveform. (Modern devices may use digital signal processing to synthesize waveforms, followed by a digital to analog converter, or DAC, to produce an analog output). The most mon waveform is a sine wave, but sawtooth, step (pulse), square, and triangular waveform oscillators are monly available as are arbitrary waveform generators (AWGs). If the oscillator operates above the audio frequency range (20 kHz), the generator will often include some sort of modulation function such as amplitude modulation (AM), frequency modulation (FM), or phase modulation (PM) as well as a second oscillator that provides an audio frequency modulation waveform.Arbitrary waveform generatorsArbitrary waveform generators, or AWGs, are sophisticated signal generators which allow the user to generate arbitrary waveforms, within published limits of frequency range, accuracy, and output level. Unlike function generators, which are limited to a simple set of waveforms。 an AWG allows the user to specify a source waveform in a variety of different ways. AWGs are generally more expensive than function generators, and are often more highly limited in available bandwidth。 as a result, they are generally limited to higherend design and test applications.Special purpose signal generatorsA tone generator and a probe for locating a specific pair of wires amongst many, for example in a punch block.In addition to the above generalpurpose devices, there are several classes of signal generators designed for specific applications.Tone generators and audio generatorsA tone generator is a type of signal generator optimized for use in audio and acoustics applications. Tone generators typically include sine waves ov