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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. Two short cable loops are also 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, Port 2 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 that share the RS-485 bus and avoids receiving stale echoed data.
3.3.2 Non RS-232 Serial Port Pinouts— LES1101A-R2
The one DB9 serial port on the LES1101A-R2 can be used as an RS-232, RS-485 or RS-422 port. By default, the LES1101A-R2 is configured
in RS-232 mode. RS-422/485 can be set entirely with the user interface (UI)—no jumpers are necessary. To return the unit to factory default
(RS-232 mode), press the Reset button.
By default, the LES1101A-R2 is configured in RS-232 mode. RS-232, RS-422, and RS-485 are software-selectable.
The DB9 pinout is shown in Table 3-3.
1 +3V
2 GND
3 RX+
4 RX-
5 TX+
6 TX-
7 +VIN
8 GND
Figure 3-3. RS-485 wiring diagram for LES1102A.
Figure 3-4. RS-232 configuration for the DB9 port on the LES1101A-R2.
Table 3-3. DB9 pinout for LES1101A-R2.
Pin:
Mode:
RS-232 RS-422 RS-485
1
DCD
2
RXD
3
TXD
4
DTR
5
GND
6
DSR
7
RTS
8
CTS
9
—
724-746-5500 | blackbox.com
—
—
RX -
—
TX +
D+
—
—
GND
GND
RX +
—
TX -
D-
—
—
422/485 422/485 SELECT
Chapter 3: Installation
D+
D-
17
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