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
7
R S 4 8 5 ( 4 - W I R E ) A N D R S 4 2 2
F
igure 5
:
RS4 85
Full D
uplex
with
T e r m i n at i o n D I P S w i t ch
S e t t i n g s
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
.
T A B L E 5 : N L 9 0 0 P R O R S 4 2 2 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
2
T-
Serial Data transmitted to radio
9
5
6
1
Female DB9
3
R-
Serial Data received by radio
4
-
No Connect
5
GND
Ground
6
-
No Connect
7
R+
Serial Data received by radio
8
T+
Serial Data transmitted to radio
9
Power
Optional Power Input
1
1.
An
inter
nal jumpe
r
mu
st be
confi
g
ured in
order to use power
over
Pi
n 9.
H A R
D W A R E F L O W
C O N T R O L
Flow control refers to the control
of data flow between the host and the NL900-PRO. It is the
method used to
handle data
in the transmit/receive buffer of
the NL900-PRO interface, and
determines how data flow
between
the
host and the NL900-PRO is throttled.
Often in
serial communication, one
device
is capable of
sending
data much faster than
the
other can receive. Flow
control
allows the slower
device
to
tell the
faster
device
to pause and resume
data transmission. (Flow control CTS and RTS are used by the NL900-PRO and
its Host, locally -
NOT over the air
. Therefore, one NL900-PRO cannot tell the
other to
slow
down or speed
up as is mentioned
above in the paragraph).
When the RTS Enable option is
selected on the Configuration Utility, the transceivers use hardware
flow
control to regulate data flow.
While using hardware flow control, the transceiver
that is ready to receive
data
sends a Clear
To Send signal to
its host (or the device it is connected
to).
On
the
other hand,
when a
transceiver has something it wants
to send
to its host, it checks the state of Ready To Send
and if it is logic
low, will send data to its host. If
RTS is
logic high, it will not
send data to its host.
These signals are sent
apart from the data itself on separate wires.