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2.3 RS-232/422/485 Interface (COM3~COM4)
The UNO-2171 offers two RS-232/422/485 serial communication inter-
face ports: COM3 and COM4. Please refer to Appendix A.4 for their pin
assignments. The default setting of COM3 and COM4 are RS-422/485.
2.3.1 16C550 UARTs with 16-byte standard
Advantech UNO-2171 comes with TI16C550 UARTs containing 16 bytes
FIFOs.
2.3.2 RS-422/485 detection
In RS-422/485 mode, UNO-2171 automatically detects signals to match
RS-422 or RS-485 networks. (No jumper change required)
2.3.3 Automatic Data Flow Control Function for RS-485
In RS-485 mode, UNO-2171 automatically detects the direction of
incoming data and switches its transmission direction accordingly. So no
handshaking signal (e.g. RTS signal) is necessary. This lets you conve-
niently build an RS-485 network with just two wires. More importantly,
application software previously written for half duplex RS-232 environ-
ments can be maintained without modification.
2.3.4 Termination Resistor (JP9)
The onboard termination resistor (120 ohm) for COM3/COM4 can be
used for long distance transmission or device matching. (Default Open.)
Pin
Description
A
TX+/TX- for COM3
Data+/Data- for COM3
B
RX+/RX- for COM3
C
TX+/TX- for COM4
Data+/Data- for COM4
D
RX+/RX- for COM4
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Chapter 2
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