Digi NS9210 - Manual (Page 49)

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Serial port B,
MEI interface
The serial (UART) port B connector, X6, is a DSUB9 male connector. This asynchronous
serial port is DTE and requires a null-modem cable to connect to a computer serial
port.
The serial port B MEI (Multiple Electrical Interface) interface corresponds to NS9215
UART port B. The line drivers are configured using switch S1.
Note that all pins on S1 contribute to the line driver settings for this port.
Serial port B pins are allocated as shown:
By default, Serial B signals are configured to their respective GPIO signals.
It is the responsibility of the driver to configure them properly.
Pin RS232
function RS232
default RS485
function RS485
default
1 DCD# GPIO51 CTS- n/a
2 RXD GPIO54 RX+ GPIO54
3 TXD GPIO58 TX+ GPIO58
4 DTR# GPIO57 RTS- n/a
5 GND GND
6 DSR# GPIO53 RX- n/a
7 RTS# GPIO56 RTS+ GPIO56
8 CTS# GPIO52 CTS+ GPIO52
9 RI# GPIO55 TX- n/a