原理图设计规范(修改)

原理图设计规范修订历史版本日期原因V0.902011/03/07创建文档i目录第1章硬件原理图设计规范······································································11.1目的···································································································11.2基本原则·····························································································11.2.1确定需求·······················································································11.2.2确定核心CPU················································································11.2.3参考成功案例················································································11.2.4对外围器件选型·············································································11.2.5设计外围电路················································································21.2.6设计时遵循的基本原则····································································21.2.7原理图审核···················································································21.2.8设计基本要求················································································31.3版面设计·····························································································31.3.1图幅·····························································································31.4元件符号及参数设置标准·······································································41.4.1常用元件位号命名规则····································································41.5元件符号·····························································································41.5.1电阻参数描述················································································41.5.2电容参数描述················································································61.5.3电感、磁珠参数描述·······································································61.5.4二极管··························································································71.5.5三极管及场效应管··········································································71.5.6其它器件·······················································································71.6元件选择·····························································································71.6.1元件库选取···················································································71.6.2元件放置要点················································································91.7多张原理图·························································································91.8版面布局····························································································101.8.1网络标号命名···············································································121.8.2总线式原理图画法·········································································121.8.3CPU画法标准···············································································131.8.4其他····························································································131.9注意··································································································141.10复杂电路设计技巧···············································································151第1章硬件原理图设计规范1.1目的原理图设计是产品设计的理论基础，设计一份规范的原理图对设计PCB、跟机、做客户资料具有指导性意义，是做好一款产品的基础。原理图设计基本要求:规范、清晰、准确、易读。制定此《规范》的目的和出发点是为了培养硬件开发人员严谨、务实的工作作风和严肃、认真的工作态度，增强硬件开发人员的责任感和使命感，提高工作效率和开发成功率，保证产品质量。1.2基本原则1.2.1确定需求详细理解设计需求，从需求中整理出电路功能模块和性能指标要求等，这些要求有助于我们器件选型和电路的设计。1.2.2确定核心CPU根据功能和性能需求制定总体设计方案，对CPU进行选型，CPU选型有以下几点要求：性价比高；容易开发：体现在硬件调试工具种类多，参考设计多，软件资源丰富，成功案例多；可扩展性好。1.2.3参考成功案例针对已经选定的CPU芯片，选择一个与我们需求比较接近的成功参考设计，一般CPU生产商或他们的合作方都会对每款CPU芯片做若干开发板进行验证，厂家公开给用户的参考设计图虽说不是产品级的东西，也应该是经过严格验证的，否则也会影响到他们的芯片推广应用，纵然参考他们设计的外围电路有可推敲的地方，CPU本身的管脚连接使用方法也绝对是值得我们信赖的，当然如果万一出现多个参考设计某些管脚连接方式不同，可以细读CPU芯片手册和勘误表，或者找厂商确认。另外在设计之前，最好我们能外借或者购买一块选定的参考板进行软件验证，如果没问题那么硬件参考设计也是可以信赖的，但要注意一点，现在很多CPU都有若干种启动模式，我们要选一种最适合的启动模式，或者做成兼容设计。1.2.4对外围器件选型根据需求对外设功能模块进行元器件选型，元器件选型应该遵守以下原则：普遍性原则：所选的元器件要被广泛使用验证过的尽量少使用冷偏芯片，减少风险；高性价比原则：在功能、性能、使用率都相近的情况下，尽量选择价格比较好的元器件，减少成本；采购方便原则：尽量选择容易买到，供货周期短的元器件；持续发展原则：尽量选择在可预见的时间内不会停产的元器件；可替代原则：尽量选择pintopin兼容种类比较多的元器件；向上兼容原则：尽量选择以前老产品用过的元器件；资源节约原则：尽量用上元器件的全部功能和管脚。21.2.5设计外围电路对选定的CPU参考设计原理图外围电路进行修改，修改时对于每个功能模块都要找至少3个相同外围芯片的成功参考设计，如果找到的参考设计连接方法都是完全一样的，那么基本可以放心参照设计，但即使只有一个参考设计与其他的不一样，也不能简单地少数服从多数，而是要细读芯片数据手册，深入理解那些管脚含义，多方讨论，联系芯片厂技术支持，最终确定科学、正确的连接方式，如果仍有疑义，可以做兼容设计。这是整个原理图设计过程中最关键的部分，我们必须做到以下几点：对于每个功能模块要尽量找到更多的成功参考设计，越难的应该越多，成功参考设计是“前人”的经验和财富，我们理当借鉴吸收，站在“前人”的肩膀上，也就提高了自己的起点；要多向权威请教、学习，但不能迷信权威，因为人人都有认知误差，很难保证对哪怕是最了解的事物总能做出最科学的理解和判断，开发人员一定要在广泛调查、学习和讨论的基础上做出最科学正确的决定；如果是参考已有的老产品设计，设计中要留意老产品有哪些遗留问题，这些遗留问题与硬件哪些功能模块相关，在设计这些相关模块时要更加注意推敲，不能机械照抄原来设计。1.2.6设计时遵循的基本原则硬件原理图设计还应该遵守一些基本原则，这些基本原则要贯彻到整个设计过程，虽然成功的参考设计中也体现了这些原则，但因为我们可能是“拼”出来的原理图，所以我们还是要随时根据这些原则来设计审查我们的原理图，这些原则包括：数字电源和模拟电源分割；数字地和模拟地分割，单点接地，数字地可以直接接机壳地（大地），机壳必须接大地；各功能块布局要合理,整份原理图需布局均衡.避免有些地方很挤,而有些地方又很松,同PCB设计同等道理；可调元件(如电位器),切换开关等对应的功能需标识清楚；重要的控制或信号线需标明流向及用文字标明功能；元件参数/数值务求准确标识.特别留意功率电阻一定需标明功率值,高耐压的滤波电容需标明耐压值；保证系统各模块资源不能冲突，例如：同一I2C总线上的设备地址不能相同，等等；阅读系统中所有芯片的手册（一般是设计参考手册），看它们的未用输入管脚是否需要做外部处理，如果需要一定要做相应处