NOVUS AUTOMATION
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CONNECTIONS
The appropriate connection to the USB-i485 Converter depends on the type of serial network: RS422, 2-wire RS485 or 4-wire RS485. The
following figure shows a description of all USB-i485 Converter connection terminals.
Fig. 03 – Device Connections
A shielded twisted-pairs cable is recommended for wiring the communication bus from the converter to all network devices. The shield should be
grounded and/or connected to the common terminals of all devices. The minimum recommended wire gauge is 24 AWG (0,2 mm
2
).
Use of a wire connecting all devices common terminals is highly recommended. Damage of the networked devices may
result if this recommendation is not followed.
RS485 or RS422 devices from different vendors or of different models may identify the communication terminals using distinct notation. The
following table shows some of this notations and its equivalence to the USB-i485 Converter.
USB-i485 CONNECTION IDENTIFICATION
Rx+ ou Tx+
Rx- ou Tx-
POPULAR RS485 AND RS422 CONNECTION IDENTIFICATION
D
D
D1
D0
B
A
D+
D-
Table 01 – Identification
5.1
HALF-DUPLEX RS485 HALF-DUPLEX (2 WIRES)
To set this mode of operation, the MOD terminal (pin 4) must be left unconnected.
This is the usual RS485 connection. A single twisted pair is used for data transmission and reception. Multiple RS485 devices are connected in a
single bus, as shown in the next figure. Devices from different vendors may use different names for the data signal terminals.
In the following figure, different identification schemes are presented for each device, with the proper connection to the USB-i485 Converter.
RS485 devices can be connected to either bus 1 or 2.
Fig. 04 – Half-Duplex RS485 (2 wires)
The common terminal (GND – pin 5) must be connected to the corresponding terminals of all network devices, to ensure the same potential in all
devices. If a common wire is not connected to all devices, all must be properly grounded according to the manufacturer recommendation. For the
USB-i485 Convert, the proper grounding terminal is pin 5 (GND).
The need to install termination resistors depends on the total length of the communication bus and the communication speed (Baud Rate). The
USB-i485 Convert has built-in termination resistors, which can be installed by wiring terminals RT1 (8) or RT2 (3) as shown in dashed lines in the
last figure.
For additional information in grounding, common wire and termination resistors, read the document
RS485 & RS422 Basic
, available on our
website
www.novusautomation.com
for download.
