Use loopbacks only if needed by device.
Notes
TXD+ 3 RXD+
TXD- 4 RXDCTs2. Many RS-485 devices have no ground connection.
In this case, leave GND pins disconnected.
2-3. Cable Selection
11/98 2-7 U3-1050
Westinghouse Proprietary Class 2C
2-3. Cable Selection
Cable for RS-232 serial communication should be multiple conductor with shield.
The shield drain wire should be used for the ground connection.
Cable for RS-422/RS-485 serial communication should be multiple twisted pairs,
overall or individually shielded. Each signal’s two differential connections should
be made within a twisted pair; signals should not cross pairs.
The RS-485 Group2 personality module includes terminating resistors which can
be placed across each signal pair by jumpering the base unit terminal block between
B14 and B15 for transmit and between A14 and A15 for receive. Refer to
Figure 2-1.

仅在设备需要时使用环回。
笔记
TXD+3 RXD+
TXD-4 RXDCTs2。许多RS-485设备没有接地连接。
在这种情况下，保持GND引脚断开。
2-3. 电缆选择
1998年11月2-7日U3-1050
西屋专有2C级
2-3. 电缆选择
RS-232串行通信电缆应为带屏蔽的多导体。
屏蔽排流线应用于接地连接。
RS-422/RS-485串行通信电缆应为多对双绞线，
整体屏蔽或单独屏蔽。每个信号的两个差分连接应
在双绞线内制作；信号不应该交叉。
RS-485 Group2个性化模块包括可以
通过将基本单元接线板跨接在
B14和B15用于传输，A14和A15之间用于接收。提到
图2-1。