Korenix JetCon Serie Guia Del Usuario página 5

4.2 RS-422/485 configuration
The JetCon 2201-w/2201-iw provides one 5-pin DIP-switch to select the RS-422/485 mode
and also provides 120 ohm line terminator selection. The configuration of DIP-switch shows
as following table. Be sure the DIP-switch is configured as right mode before make the
RS-422 or RS-485 connection.
Description
RS-422
RS-485 4-wire
RS-485 2-wire
RX +/- Terminator (120Ω)
RX+/- Biasing (150KΩ)
RX+/- Biasing (1KΩ)
In an idled multi-drop RS-485 network, all nodes are in listen (receive) mode. Under this
condition there are no active drivers on the network. All drivers are tri-stated. Without anything
driving the network, the state of the line is unknown. The JetCon 2201 provides biasing
resistor select function to offer and keep 200 mV at the RX+ and RX-. If the network node up
to 32, the first or last node need turn-on the Biasing resistor to keep the last bit state at RX+/- .
The 120Ω terminator is used to match the line impendence, when the line impendence is
mismatched, the transmitted signal is not absorbed and a portion is reflected back to the
transmission line and interference the communication. Also, the terminator only applies at first
and last node in a multi-drop RS-485 network.
4.3 Connecting RS-422 and RS-485
The JetCon 2201 supports one 7-pin removable terminal block for RS-422/RS-485 2-wire and
4-wire communication.
In the following diagram shows the wiring architecture of RS-422, RS-485 2/4-wire.
The RS-485 support 2/4-wire master-slave communication mode, the master-slave type
architecture has one node that issues commends to each slave node and process the
responses that from slave. Slave node won't transmit data without request from master node.
In the multi-drop serial network, each slave should have its own unique address.
SW4
SW1 SW2 SW3
Off Off X X
On Off X X
On On X X
X X On X
X X X Off
X X X On
SW5
X
X
X
ON
X
Off
On
1 2 3 4 5