Termination; Networking; Flow Control; Hardware Flow Control - Lantronix SCS Reference Manual

Ports

8.10.3 Termination

RS-485 connections must be terminated properly in order to work. Termination is necessary when using
long cable runs, although only end nodes should be terminated. The termination option is disabled by
default.
Local>> DEFINE PROTOCOLS RS485 TERMINATION ENABLED
8.10.4 RS-422 Networking
The SCS is compatible with RS-422 networks in four-wire RS-485 mode. Connect the SCS to a single slave
device using a swapped cable, as shown below, and configure the SCS as if you were going to use it for
four-wire RS-485 networking.

8.11 Flow Control

Flow control enables two connected devices to control the amount of data transmitted between them. When
flow control is enabled on an SCS port and a connected device such as a modem, flow control ensures that
data sent from the sending device does not overflow the receiving device's buffers. Consider the following
example.
An SCS port is connected to a modem. The SCS port transfers data to the modem at 115,200 bits per second,
but the modem can only send data over the phone line at 15,000-30,000 bits per second. In a short period of
time, the modem's buffer fills with data. The modem sends a signal to the SCS to stop sending data, and the
SCS does not send data until it receives a signal from the modem that it can receive data again.
The SCS supports hardware and software flow control. The hardware flow control option is RTS/CTS and
the option for software flow control is XON/XOFF. Both flow control methods are described below.
When the SCS is communicating with a device, the SCS and the device must
Note:
agree on the type of flow control used.

8.11.1 Hardware Flow Control

When hardware flow control is used, the flow of data is controlled by two serial port signals (typically RTS
and CTS). Two connected devices will assert and deassert RTS and CTS to indicate when they are ready to
accept data.
Figure 8-46: Enabling RS-485 Termination
Figure 8-47: RS-422 Connection
Shield
TX-
TX
TX+
RX+
RX
RX-
Shield
Master
(SCS)
Shield
RX-
RX+
TX+
TX-
Shield
8-18
Flow Control
RX
TX
Slave