学会不画电路图，不用网络表，用手工布线。从而加深对PCB电路版图设计的理解。
标签： PCB
上传时间： 2013-11-06
上传用户：lyson
USB接口控制器参考设计,xilinx提供VHDL代码 usb xilinx vhdl ; This program is free software; you can redistribute it and/or modify ; it under the terms of the GNU General Public License as published by ; the Free Software Foundation; either version 2 of the License, or ; (at your option) any later version. ; ; This program is distributed in the hope that it will be useful, ; but WITHOUT ANY WARRANTY; without even the implied warranty of ; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ; GNU General Public License for more details. ; ; You should have received a copy of the GNU General Public License ; along with this program; if not, write to the Free Software ; Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
上传时间： 2013-10-29
上传用户：zhouchang199
注:1.这篇文章断断续续写了很久,画图技术也不精,难免错漏,大家凑合看.有问题可以留言. 2.论坛排版把我的代码缩进全弄没了,大家将代码粘贴到arduino编译器,然后按ctrl+T重新格式化代码格式即可看的舒服. 一、什么是PWM PWM 即Pulse Wavelength Modulation 脉宽调制波，通过调整输出信号占空比，从而达到改 变输出平均电压的目的。相信Arduino 的PWM 大家都不陌生，在Arduino Duemilanove 2009 中，有6 个8 位精度PWM 引脚，分别是3, 5, 6, 9, 10, 11 脚。我们可以使用analogWrite()控 制PWM 脚输出频率大概在500Hz 的左右的PWM 调制波。分辨率8 位即2 的8 次方等于 256 级精度。但是有时候我们会觉得6 个PWM 引脚不够用。比如我们做一个10 路灯调光， 就需要有10 个PWM 脚。Arduino Duemilanove 2009 有13 个数字输出脚，如果它们都可以 PWM 的话，就能满足条件了。于是本文介绍用软件模拟PWM。 二、Arduino 软件模拟PWM Arduino PWM 调压原理：PWM 有好几种方法。而Arduino 因为电源和实现难度限制，一般 使用周期恒定，占空比变化的单极性PWM。 通过调整一个周期里面输出脚高/低电平的时间比（即是占空比）去获得给一个用电器不同 的平均功率。 如图所示，假设PWM 波形周期1ms（即1kHz），分辨率1000 级。那么需要一个信号时间 精度1ms/1000=1us 的信号源，即1MHz。所以说，PWM 的实现难点在于需要使用很高频的 信号源，才能获得快速与高精度。下面先由一个简单的PWM 程序开始： const int PWMPin = 13; int bright = 0; void setup() { pinMode(PWMPin, OUTPUT); } void loop() { if((bright++) == 255) bright = 0; for(int i = 0; i < 255; i++) { if(i < bright) { digitalWrite(PWMPin, HIGH); delayMicroseconds(30); } else { digitalWrite(PWMPin, LOW); delayMicroseconds(30); } } } 这是一个软件PWM 控制Arduino D13 引脚的例子。只需要一块Arduino 即可测试此代码。 程序解析：由for 循环可以看出，完成一个PWM 周期，共循环255 次。 假设bright=100 时候，在第0~100 次循环中，i 等于1 到99 均小于bright，于是输出PWMPin 高电平； 然后第100 到255 次循环里面，i 等于100~255 大于bright，于是输出PWMPin 低电平。无 论输出高低电平都保持30us。 那么说，如果bright=100 的话，就有100 次循环是高电平，155 次循环是低电平。 如果忽略指令执行时间的话，这次的PWM 波形占空比为100/255，如果调整bright 的值， 就能改变接在D13 的LED 的亮度。 这里设置了每次for 循环之后，将bright 加一，并且当bright 加到255 时归0。所以，我们 看到的最终效果就是LED 慢慢变亮，到顶之后然后突然暗回去重新变亮。 这是最基本的PWM 方法，也应该是大家想的比较多的想法。 然后介绍一个简单一点的。思维风格完全不同。不过对于驱动一个LED 来说，效果与上面 的程序一样。 const int PWMPin = 13; int bright = 0; void setup() { pinMode(PWMPin, OUTPUT); } void loop() { digitalWrite(PWMPin, HIGH); delayMicroseconds(bright*30); digitalWrite(PWMPin, LOW); delayMicroseconds((255 - bright)*30); if((bright++) == 255) bright = 0; } 可以看出，这段代码少了一个For 循环。它先输出一个高电平，然后维持(bright*30)us。然 后输出一个低电平，维持时间((255-bright)*30)us。这样两次高低就能完成一个PWM 周期。 分辨率也是255。 三、多引脚PWM Arduino 本身已有PWM 引脚并且运行起来不占CPU 时间，所以软件模拟一个引脚的PWM 完全没有实用意义。我们软件模拟的价值在于：他能将任意的数字IO 口变成PWM 引脚。 当一片Arduino 要同时控制多个PWM，并且没有其他重任务的时候，就要用软件PWM 了。 多引脚PWM 有一种下面的方式： int brights[14] = {0}; //定义14个引脚的初始亮度，可以随意设置 int StartPWMPin = 0, EndPWMPin = 13; //设置D0~D13为PWM 引脚 int PWMResolution = 255; //设置PWM 占空比分辨率 void setup() { //定义所有IO 端输出 for(int i = StartPWMPin; i <= EndPWMPin; i++) { pinMode(i, OUTPUT); //随便定义个初始亮度,便于观察 brights[ i ] = random(0, 255); } } void loop() { //这for 循环是为14盏灯做渐亮的。每次Arduino loop()循环， //brights 自增一次。直到brights=255时候，将brights 置零重新计数。 for(int i = StartPWMPin; i <= EndPWMPin; i++) { if((brights[i]++) == PWMResolution) brights[i] = 0; } for(int i = 0; i <= PWMResolution; i++) //i 是计数一个PWM 周期 { for(int j = StartPWMPin; j <= EndPWMPin; j++) //每个PWM 周期均遍历所有引脚 { if(i < brights[j])\ 所以我们要更改PWM 周期的话，我们将精度（代码里面的变量：PWMResolution）降低就行，比如一般调整LED 亮度的话，我们用64 级精度就行。这样速度就是2x32x64=4ms。就不会闪了。
上传时间： 2013-10-23
上传用户：mqien
In today’s IT environment, Java is a leading technology in the world of enterprise development. As management demands more from technology, complexity in infrastructure seems to grow exponentially, leaving many unable to keep up with the demands of such a fast-paced world. These complexities can be seen in the over-evolving Java 2 Enterprise Edition (J2EE) specifications. This unnecessary complexity drove us to discover ways of simplifying development.
标签： environment development enterprise technology
上传时间： 2013-12-24
上传用户：Zxcvbnm
21天学会用JAVA开发网络游戏 书籍语言： 简体中文 书籍类型： 程序设计 授权方式： 免费软件 书籍大小： 287 KB 书籍等级： 整理时间： 2004-11-3 20:41:10 With all of the media attention that is focused on the Internet and the World Wide Web, figuring out exactly what they are all about is sometimes difficult. Are they just a neat new way to market products or will they truly offer us a new medium of communication that will someday surpass even televisions and telephones? The answer is, who knows? Unfortunately, the ultimate use for the Internet is still unknown. This is because it is still in such a state of flux that it s pretty much impossible to accurately predict where it will end up. However, you can look at the evidence of what is there now and gain some insight into what the Internet might become, at least in terms of games.
上传时间： 2013-12-20
上传用户：天诚24
The code is fairly straightforward, except perhaps for the call to convertColumnIndexToModel. That call is necessary because if the user moves the columns around, the view s index for the column doesn t match the model s index for the column. For example, the user might drag the Vegetarian column (which the model considers to be at index 4) so it s displayed as the first column — at view index 0. Since prepareRenderer gives us the view index, we need to translate the view index to a model index so we can be sure we re dealing with the intended column
标签： convertColumnIndexToModel straightforward perhaps fairly
上传时间： 2013-12-10
上传用户：it男一枚
fs44b0x_usb -- usb 测试程序 PC机部分的软件 1) LEDDEMO -- 控制 FS44B0X板上三个LED的程序 2) D12_DRIVER_FOR_WIN98 -- USB芯片WIN98的驱动程序 3) D12_DRIVER_FOR_WINXP -- USB芯片WINXP的驱动程序 FS44B0X板的USB固件程序--源代码 USB_DEMO 使用方法： 1）在SDT2.51里调入usb_demo.axf, 运行。 2）接上usb电缆，安装win98的d12驱动程序（或者winxp的d12驱动程序） 3) 运行 LEDDEMO ，用鼠标点击led1, led2, led3,可以看到FS44B0X板上三个LED亮灭。
标签： DRIVER_FOR_WIN LEDDEMO x_usb 44
上传时间： 2014-01-19
上传用户：李梦晗
Expert Choice represents a significant contribution to the decision making process 工t assists a decision maker in solving complex problems involving many criteria and several courses of action . An Expert Choice solution to a problem reflects the expertise of the decision maker , not the computer . Behavioral scientists have spent many years studying the human mind and how it makes decisions . They have found that humans are influenced by their previous experiences and this causes them to have biases . Basic instincts , preferences and environmental factors also play key roles in how we analyze data and make decisions . There 15 way to remove these factors from human decision making , nor would we necessarily want to , but as the problems of our world become more and more complex , it 15 necessary for us to employ a framework to help make more logical and less biased decisions while still taking our feelings and intuition into consideration .
标签： contribution significant represents decision
上传时间： 2015-06-02
上传用户：gmh1314
红外线遥控器读码软件，显示红外线波型，读取并保存码 IR Remote Control Unit Code Read System 产品详细描述： 能够像显示器一样显示红外线码的波型 可以读多达１５０种格式的红外线码 显示红外线码的时间非常准确，误差只有几个微秒。 具有错误检测功能 保存红外线码功能 自动识别码的格式 比较样机与所写的新软件的遥控器码的异同 具体情况请访问本网站：http://www.crzman.com/IR_Reader.htm Display the Infrared wave on the software like oscillograph. Can read more than 150 kinds of infrared code format Display the Infrared time and the tolerance no more than many us. Have error detect function Save Infrared code function Auto identify code s format Compare the code from sample and new Remote Control Unit code) Detail instance please visit address: http://www.crzman.com/IR_Reader.htm
上传时间： 2015-07-03
上传用户：ccclll
用delphi编的，很精确的定时，精确度可以少于us.
标签： delphi
上传时间： 2015-07-11
上传用户：qweqweqwe
