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Rs-485 operating information – Remote Processing CX-10 User Manual

Page 22

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SERIAL PORTS

BASIC

SECTION 4

Page 4-5

Modbus Master

RS-485

Additional CX-10 or
modbus device

Additional CX-10 or
modbus device

CX-10
with RF modem

CX-10
with RF modem

RS-485

RS-232

Optional CX-10 or other
modbus devices

Optional CX-10 or other
modbus devices

Optional CX-10 or other
modbus devices

Optional CX-10 or other
modbus devices

Figure 4-5 Multiple Slave with RF Modem

A large number of slaves can be connected in different
manners. Note that one slave can be connected via RS-
232 to the remote slave, on the right side of the drawing.
If only one CX-10 is connected to the modbus master, it
may be through RS-232 or RS-485 as shown in Figure 4-
2.

These are just some of the ways the CX-10 can be
connected in a network. Contact Remote Processing to
discuss your situation if you have any questions.

COM3 Baud Rate
COM3 baud rate is set by register 4813. Default is
19200 (value of 5). Table below shows possible baud
rates and the corresponding number to be written to
register 4813.

Register 4813 value

Baud rate

2

2400

3

4800

4

9600

5 (default)

19200

6

38400

7

57600

RS-485 OPERATING INFORMATION

The CX-10 has a so called 2-wire RS-485 port. A third
wire for ground is necessary. Signal lines are designated
as 485A and 485B. 485A idles high while 485B line

idles low.

Normally this port is in receive mode. However, any
transmit output via COM3 or the RF modem changes its
mode to transmit.

A master modbus device may be connected to the RS-
485 port, enabling networking the CX-10 with other CX-
10's or other modbus devices. The only requirement is
that each modbus device have its own ID (which is a
modbus requirement anyway).

RS-485 Termination network
RS-485 is designed to operate over long distances (>
1000 meters) at high speed. Due to cable lengths and
high data rates, signal ringing will occur. A termination
network with pull up and pull down resistors is included
on the CX-10 . The CX-10 presents a 120 ohm
impedance to a signal source.

The other 485 device should have a terminator installed.
This will present a balance, 60 ohm line impedance. If
more than one device with a terminator is installed, the
device between the two farthest units should have its
terminator removed.

RS-485 transmitter turn-off
The RS-485 transmitter is controlled by the operating
system or RF modem, if sending. The 485 transmitter is
turned off when the last character is sent.