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Serial Port Pinouts –LES1508A
Each serial RJ-45 ports on these models can be software selected to be RS-232, RS-422 or RS-485.
• For RS232 they have the Cisco pinout
• For RS-422 mode it’s 4-wire full duplex transmit
on TX+/TX- pair, receive on RX+/RX- pair with
the following pinout
• For RS-485 it’s 2-wire half duplex
For the RS-485 option, to provide half duplex ‘party-line’ communications over a 2-wire bus (D+/D-), two short
cable loops are required between the RX+/TX+ pins (pins 1 and 6) and RX-/TX- pins (pins 3 and 8) on the serial
RJ-45 cable connector. This is because the -I model uses universal differential transceivers that support 4-wire
(RS-422) and 2-wire (RS-485) operation. In RS-485 mode, the -I model listens on the 2-wire bus for receive data
until it is required to send data. In RS-485 send mode it stops receiving, enables its transmitters when there is
data to be sent, transmits the data and returns to receive mode. This eliminates the possibility of collisions with
other devices which share the RS-485 bus and avoids receiving bogus stale echoed data.
Serial Port Pinouts –LES1102A
The LES1102A supports (by default) two RS232 ports on Port 1 and Port 2 DB9 connectors. Port 2 on the LES1102A can
also be software selected to be an RS485 or RS422 port connected through the screw terminal block (shown below):
1 +V DC IN
2 GND
3 RX+
4 RX-
5 TX+
6 TX-
7 +3.3V DC OUT
8 GND
• RS-422 uses a full duplex transmit on TX+/TX- pair, receive on RX+/RX- pair
• RS-485 uses half duplex over single pair. The LES1102A supports half duplex ‘party-line’ communications over a
2-wire RS-485 bus (D+/D-). This is enabled by choosing the RS-485 option (instead of RS-232 or RS-422) for
“Signaling Protocol” from the “Serial Port: Configuration” link on the Web management console. In addition two
short cable loops are required between the RX+/TX+ pins and RX-/TX- pins. This is because the LES1102A uses
universal differential transceivers that support 4-wire (RS-422) and 2-wire (RS-485) operation. In RS-485 mode,
Port2 on the LES1102A listens on the 2-wire bus for receive data until it is required to send data. In RS-485 send
mode it stops receiving, enables its transmitters when there is data to be sent, transmits the data and returns to
receive mode. This eliminates the possibility of collisions with other devices which share the RS-485 bus and
avoids receiving stale echoed data.
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