orCad Capture中instance 和 occurrences概念的理解[转载]

心间

笔者昨晚在批量替换和更新元件封装的时候，遇到很迷惑的问题，无论怎么搞，批量更新的Footprint也不能在元件的Properties中可见，这就意味着只能手工一个个去修改，或者按照Page的属性去修改，将近200个元件，其任务量可想而知。

在仔细的比对了OrCAD Capture CIS16.3 和16.6版本的区别之后终于找到了问题的所在，首先咱们来搞清楚这两个概念吧。

instance

n.  实例；情况；建议
occurrence
n.  发生；出现；事件；发现

当你在原理图库中调用了一个元件，比如这个元件是一个电容CAP，当你在Schematic Page1中第一次放置这个元件的时候会产生一个instance和occurrence，当你再次放置一个CAP时，这时候会再产生一个occurrence。

从这里可以看出：instance表示了元件的公有属性，表明了这一类元件；而occurrence表示一个实例，表示的是这一个元件，一个元件对应着一个occurrence，一个occurrence表示了一个元件的私有属性。

举个例子，选中Page1中的一个CAP右击Edit Part就可以修改occurrence得到一个instance，这是一个新的instance，此时我们选择update current，在Design Cache中就多了一个名字叫CAP 的instance，来源地址为本设计的数据库，这样在你的设计中就有两个CAP的instance，因为这两个元件的属性不同，当你再次放置一个CAP的时候，就可以选择这两者中的任意一个。

说说我在批量更新元件封装Footprint遇到的问题并且如何解决的，因为网上的教程和书籍大部分都是基于16.3的，所以这样错误也在所难免。  （PS:昨天好像是软件出问题了，这会儿重新新建工程并且导入好像没有发生什么问题。）

切换到项目管理窗口，选择整个设计的入口-》Edit-》Browse-》Parts

这个地方的默认选项是 use occurrences ，但是在16.3版本却是

我个人的想法，既然是修改每个元件的属性，就应该修改use occurrences ，所以这里推荐上图的做法，估计下图是以前的版本不够完善。

再来看看导出materials时，应该选择什么：

因为咱们导出的是一类元件，一类元件下面饱含许多instance，所以这里选择occurrence，我们经常看到一个阻值的电阻一栏后面有很多，这里差不多就是这个道理。

最后附上Cadence16.6 官方help文件里面关于这方面理解，供大家查阅，基本上和我说的一致。

Part Instances and Occurrences
A is a part you have placed on a schematic page. A part is created each time the part instance occurs in a schematic that is within the design hierarchy. So, for example, placing a part on a schematic page in your design creates both an instance and an occurrence. You can assign properties to the part instance, in which case the property (and its associated value) will "shine through" to each part occurrence unless the value is specifically replaced by a value on an individual part occurrence. graphically illustrates the state of instance and occurrence properties.
The instance property values shines through to the occurrence as long as the occurrence property values have not been edited in any way. When you explicitly edit an occurrence property value or when Capture modifies it via one of its tools, the occurrence values overrides the instance value. Only the occurrence value will be placed in the netlist.
If you...
The result will be...
place a part on an unused page in your design
only instance properties on that part.
place one part in the root schematic
one set of instance properties and one set of occurrence properties on that part.
do not modify the occurrence properties on an object
instance properties will "shine through" on the occurrence. The instance properties themselves may be shining through from the library definition (or design cache if the two differ
edit a part in a library
no effect on the part in any project.
Use the or to bring library changes into a design.

How Capture uses instance and occurrence properties
The type of property you update or use in Capture depends on the type of project in which you are working. If you are working with an FPGA project or a PSpice project, Capture allows you a choice, but defaults to update instances when you use the Annotate, Update Properties or Export Properties commands. It is best that you use instances to create Cross Reference and Bill of Materials reports, as well.
When you work with a PCB or schematic project, it is best to update occurrences when you use the Annotate, Update Properties, and Export Property commands. In these projects, Capture also uses occurrences to create reports with Cross Reference and Bill of Materials.
While modifying occurrence properties, open only one occurrence at a time.


The EDIF 2 0 0, VHDL, and Verilog netlist formats generate true hierarchical netlists. Capture uses the instance property values on nets and parts when it generates a netlist for a design with one of these formats. All other netlist formats in Capture produce flat netlists and use occurrence property values.
Preferred modes for design processing
Capture determines and recommends a preferred mode for processing your design based on the type of project flow, type of design with respect to complex or simple hierarchy, and whether occurrence properties already exist on the design.
The is an example of where you can choose to use instances or use occurrences as the preferred mode.
Use instances
If you are in an FPGA, PSpice, or digital simulation project, or if your design does not have occurrence properties.
Use occurrences
If your design has at least one schematic used multiple times or a schematic from an external library. Using occurrences is also the preferred mode if the design already has some occurrence properties.