CL4490 Hardware Integration Guide
Version 1.0
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14
Laird Technologies
RS485 (4-Wire) and RS422
1.
Termination is a 120 ohm resistor.
Figure 10: RS485 Full Duplex and Termination DIP Switch Settings
Table 7: CL4490-PRO RS422 Pinout
DB9 Pin
Signal Name
Description
1
-
No Connect
2
T-
Serial Data transmitted to radio
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 internal jumper must be configured in order to use power over Pin 9.
Hardware Flow Control
Flow control refers to the control of data flow between the host and the CL4490. It is the method used to
handle data in the transmit/receive buffer of the CL4490 interface and it determines how data flow between
the host and the CL4490 throttles. 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. Because flow control signals CTS and RTS are used by the CL4490 and
its host
locally
(rather than over the air), one CL4490 cannot tell the other CL4490 to slow down or speed up.
The CL4490 sets the Clear to Send (CTS) line logic Low when it is able to accept data over the serial interface
from the host, and alternately sets the CTS line logic High to signal that it is not ready to accept additional
data from the host. By default the CTS signal on the CL4490 is always operational. When the
RTS Enable
option is selected through the Configuration Utility, the CL4490 checks the state of Ready to Send (RTS)
before sending data over the serial interface to the host. If RTS is logic Low, the CL4490 sends data over the
serial interface to its host. If RTS is logic High, it does not send data to its host. These signals send apart from
the data itself on separate wires.
Note: CTS is always enabled by default. RS485 Interface does not support Hardware flow control.
RTS is high by default on the CL4490. If RTS Enable is enabled, the CL4490 will not transmit data
out the serial interface unless the RTS line is driven low by the OEM host.
DB9 female
connector
