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Installing Peripherals
RS-485 - Party Line Operation: The RS-485 offers the ability to transmit and
receive over the same pair of wires (RX outputs: pins 3 and 4), and share the same
communication line with multiple stations. To ensure this configuration, only one system
takes the control of the communication line at the time.
VCC
EN ABLE
The RS-485 protocol offers some advantages such as increased speed over long
distances, improved reliability over similar RS-232 setups, ability to share the
transmission line, less cabling requirements than RS-422 protocol.
Upon power-up or reset, the transceiver is by default in "receiver mode" to prevent
undesired perturbation on the line.
In RS-485 mode, only both ends of the network must be terminated (120 Ohms
resistors). Termination resistors are available: If the board is installed at one end of the
network, these resistors may be installed using the W2 and W3 jumpers.
Pinout: When configured for RS-422/485 communication mode, the pin assignation for
the onboard Serial Port 2 (J7) appears as follows:
O nboard
10-pin H eader
1
2
9
10
VCC
RXD2
1
2
3
TXD2
4
I/O
Pin #
Sign al
I
D C D
1
I/O
R X (-)
3
O
T X (-)
5
O
D T R
7
-
G N D
9
O nb oard S erial P o rt C onne ctor s et a s R S -485
8-5
S ER IA L PO R T 2
10 -PIN HE A D ER
120 ohms
7
6
Pin #
I/O
Signal
2
D S R
I
4
R X (+ )
O
6
T X (+ )
I
8
R I
I
10
N .C .
-
3
RX-
4
RX+
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