Rs-232/422/485 Interface (Com3~Com4); 16C550 Uarts With 16-Byte Standard; Rs-422/485 Detection; Automatic Data Flow Control Function For Rs-485 - Advantech UNO-2000 Series User Manual

2.3 RS-232/422/485 Interface (COM3~COM4)

The UNO-2182 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-2182 comes with TI16C550 UARTs containing 16 bytes
FIFOs.

2.3.2 RS-422/485 detection

In RS-422/485 mode, UNO-2182 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-2182 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 (CN21)

The onboard termination resistor (120 ohm) for COM3/COM4 can be
used for long distance transmission or device matching. (Default Open.)
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