Advantech UNO-1140/F, Руководство пользователя

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2.2.3 Terminal Resistor Setup for RS-485
The onboard termination resistor (120 Ohm) for each COM port can be
used for long distance transmission or device matching. (Default Open.)
Each terminal resistor responds to different channels for RS-422/485.
Usually, these resistors are needed for both ends of the communication
wires and the value of the resistors should match the characteristic imped-
ance of the wires used.
2.3 COM5~COM8: RS-485 Interfaces (UNO-1140F)
The UNO-1140F offers four isolated RS-485 serial communication interface
ports on the top side, and they are COM5 ~ COM8. Please refer to A.3 for pin
assignments and Table 2.2 for the setting of Terminal resistors.
These COM ports come with Oxford OXmPCI954 UARTs containing 128
bytes FIFOs. These upgraded FIFOs can greatly reduce CPU overhead.
The same as COM1~COM4, UNO-1140F COM5~COM8 RS-485 mode can
also automatically senses the direction of incoming data and switches its
transmission direction accordingly.
Table 2.2: Terminal Resistor Settings for COM Port
COM Jumper Pin Status
COM1 JCOM1234 1-2 Close to add 120 Ohm terminal resistor
on Data+/Data- of RS-485, default is
Open
COM2 3-4
COM3 5-6
COM4 7-8
COM5 JCOM5678 1-2
COM6 3-4
COM7 5-6
COM8 7-8