HART375里面这几段话的含义

学习自控仪表

看到王天泽在现场仪表版说的HART375的极性问题，但是都是英文，看不懂啊。原文：手持终端的两根通讯线有极性吗
Connect the 375 Field Communicator with the appropriate connectors in parallel with the instrument or load resistor. The HART connections are not polarity sensitive.
In order for the 375 Field Communicator to function properly, a minimum of 250 ohms resistance must be present in the HART loop. There are three terminals on the top of the 375 Field Communicator.
Two of them are red and one of them is black. Each red terminal is a positive connection for its protocol. The black terminal is a common shared by both protocols. There is an access door to ensure that only one pair of terminals is exposed at any one time; see Figure 3-1. There are several markings to indicate which pair of terminals is for which protocol.