User manual
C H
A P T E R 3
- S
E
R I
A L
I N T E R F A C E
6
R S
4 8
5 ( 2 -
W
I
R
E )
The
RS-485 interface uses a Differential
Data
Transmission
that
can help nullify the effects of ground
shifts
and induced noise signals that
can appear
as common mode voltages on a network.
The NL900PRO implements a RS-485 (2-wire Half Duplex) multi-drop interface. Typically, a RS-485 bus will
consist of a master and several slaves. The nodes will have unique addresses and can send addressed
packets to specific nodes. Because the bus is half duplex, no two nodes should try to talk at the same time.
The
NL900PRO does
not have a RS-485 address, therefore, it
will transmit all RS-485 traffic over
the
RF.
Conversely, as
soon as
a
NL900PRO receives a packet
over the RF, it will transmit the
packet
over the RS-
485 bus.
F i g u r e
4
:
R S 4 8 5
H a
l f
D u p l e x
w i t h
Termination
D I P
S w i t ch
S et tings
ON
ON
1
2 3
4
5
6
1
2 3
4
5
6
With Termination
1
Without Termination
1.
Termina
tion i
s a 1
20 ohm
resi
stor
between TR- a
n
d TR+.
T A B L E 4 : N L 9 0 0 P R O R S 4 8 5 P I N O U T
D B
9 P I N
S
I G N A L N A M E
D E S
C R I P T I O N
1
-
No Connect
9
5
6
1
Female DB9
2
TR-
Serial Data transmitted to &
received from radio
3
-
No Connect
4
-
No Connect
5
GND
Ground
6
-
No Connect
7
-
No Connect
8
TR+
Serial Data transmitted to &
received from radio
9
Power
Optional Power Input
1
1.
An i
n
terna
l jumper must be configured in o
r
der
to use power
over
Pi
n 9.