最近在学习EtherNET/IP，PATH不太明白，翻了翻规范，在这里记个笔记。下面的叙述可能是中英混合，有一些是规范中的原文我直接搬过来的。我翻译的不准确。

Segment

PATH是CIP Segment中的一个分类。要了解PATH先要了解Segment

参考规范卷1，附录C-1
A CIP segment is a stream of encoded items used to reference, describe, and/or configure a specific CIP entity。

CIP Segment 分类如下
• Port segment – used for routing from one subnet to another
• Logical segment - logical reference information (such as class/instance/attribute IDs)
• Network segment - specifies network parameters needed to transmit on some networks
• Symbolic segment - symbolic name
• Data segment - embedded data (such as configuration data)

Segment使用一个字节编码，包含Segment类型和格式。格式根据Segment类型不同而不同

PATH

PATH属于其中的Logical segment.
一个PATH包含多个Logical segment，在一个object中引用其他object的类，实例，属性。

PATH用途如下
• In Connection and Connection Manager Objects, paths indicate the object(s) to/from which
I/O data is moved.
• In Assembly Objects, paths indicate the attributes in other objects which are used to form
the assembled I/O data.
• In Parameter Objects, paths indicate the actual attribute in another object which is being
described by the Parameter Object.

PATH结构如下，需要注意的是，这里的PATH只有一个段属性，PATH可以包含多个段属性，访问到更深入的数据。后面会给例子。

logical segment 编码如下

举例

举三个例子

• 8-Bit Service ID Segment (0x38)
• Electronic Key Segment (0x34)（The Electronic Key segment shall be used to verify/identify a device）
•