TRB142 RS232

Summary

The RS232 function is designed to utilize the serial interface of the device. Serial interfaces provide a possibility for legacy devices to gain access to IP networks. This chapter is an overview of the RS232 section.

RS232 connector pinout

The RS232 connector type on this device is a DCE female. DCE stands for Data Communication Equipment.

RS232 connector pinout
Pin	Name	Description
2	RXD	Output
3	TXD	Input
5	GND	-
7	RTS	Input
8	CTS	Output

Cables

There are two types of RS232 serial devices: DTE and DCE. DTE typically refers to the serial port on a PC or terminal, while DCE refers to communication devices. Connectors mounted on DTE are likely to be male, and those mounted on DCE are likely to be female.

This device is DCE and has a female connector.

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To connect a standard DTE device, use a straight-through Female/Male RS232 cable:

See straight cable pinout below:

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To connect another DCE device to RUT955, a Null-modem (crossed) Male/Male cable should be used:

See straight crossed cable pinout below:

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Maximum cable length is 15 meters or the cable length equal to a capacitance of 2500 pF (for a 19200 baud rate). Using lower capacitance cables can increase the distance. Reducing communication speed can also increase maximum cable length.

RS232 Configuration

The RS232 Configuration section is used to configure the parameters of the RS232 serial connection. Parameters used should be selected in accordance with the needs of the user and the type of device connected via the RS232 port.

The figure below is an example of the RS232 Configuration section and the table below provides information on the fields contained in that section:

field name	value	description
Enabled	yes | no; Default: no	Enables the RS232 service
Baud rate	300 | 1200 | 2400 | 4800 | 9600 | 19200 | 38400 | 57600 | 115200; Default: 115200	Data rate for serial data transmission (in bits per second)
Data bits	5 | 6 | 7 | 8; Default: 8	Number of data bits for each character
Parity	None | Odd | Even; Default: None	In serial transmission, parity is a method of detecting errors. An extra data bit is sent with each data character, arranged so that the number of 1 bits in each character, including the parity bit, is always odd or always even. If a byte is received with the wrong number of 1s, then it must have been corrupted. However, an even number of errors can pass the parity check. None (N) - no parity method is used Odd (O) - the parity bit is set so that the number of "logical ones (1s)" has to be odd Even (E) - the parity bit is set so that the number of "logical ones (1s)" has to be even
Stop bits	1 | 2; Default: 1	Stop bits sent at the end of every character allow the receiving signal hardware to detect the end of a character and to resynchronise with the character stream. Electronic devices usually use one stop bit. Two stop bits are required if slow electromechanical devices are used
Flow control	None | RTS/CTS | Xon/Xoff; Default: None	In many circumstances a transmitter might be able to send data faster than the receiver is able to process it. To cope with this, serial lines often incorporate a "handshaking" method, usually distinguished between hardware and software handshaking. RTS/CTS - hardware handshaking. RTS and CTS are turned OFF and ON from alternate ends to control data flow, for instance when a buffer is almost full Xon/Xoff - software handshaking. The Xon and Xoff characters are sent by the receiver to the sender to control when the sender will send data, i.e., these characters go in the opposite direction to the data being sent. The circuit starts in the "sending allowed" state. When the receiver's buffers approach capacity, the receiver sends the Xoff character to tell the sender to stop sending data. Later, after the receiver has emptied its buffers, it sends an Xon character to tell the sender to resume transmission
Serial type	Console | Over IP | Modem | Modbus gateway | NTRIP client; Default: Console	Serial connection type. More information on each serial type can be seen below or by clicking on a link in the value section
Echo	yes | no; Default: no	Toggles RS232 echo ON or OFF. RS232 echo is a loopback test usually used to check whether the RS232 cable is working properly

Serial types

An RS232 serial connection can function in different ways depending on user needs and what devices are connected to the RS232 port. This section of the chapter is an overview of all different RS232 serial types.

Console

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In Console mode the serial interface is set up as a Linux console that can be used to control the device (much like a regular SSH connection, except established via RS232). It can be used for debugging purposes, to get the status of the device or to control it. Click here to find a guide on how to set up RS232 in console mode.

Over IP

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In Over IP serial type the device provides a connection to a TCP/IP network for the devices connected via the serial interface. The figure below is an example of available configuration fields for the Over IP serial type and the table below provides information on these fields:

field name	value	description
Protocol	TCP; Default: TCP	Protocol used in the communication process
Mode	Server | Client | Bidirect; Default: Server	Device's role in the connection: Server - the device waits for incoming connections Client - the device initiates the connection Bidirect - acts as client by default but waits for incoming connections at the same time
No leading zeros	yes | no; Default: no	When checked, indicates that the first hex zeros should be skipped
Client settings: Server address	ip | host; Default: none	IP address or hostname of the server that the client will connect to
Client settings: TCP port	integer [0..65535]; Default: none	Server's port number
Client settings: Reconnect interval (s)	integer; Default: none	Time period (in seconds) between reconnection attempts in case a connection fails
Server settings: TCP port	integer [0..65535]; Default: none	Internal TCP port number used to listen for incoming connections
Server settings: Timeout (s)	integer; Default: none	Disconnects clients after they remain inactive for an amount time (in seconds) specified in this field
Output	OC Output | Relay Output; Default: OC Output	Output to indicate that the application switched from client (default) to server state (this field becomes visible only in Bidirect mode)
Output state	1 | 0; Default: 0	Output state value during which the application reverts to server mode (this field becomes visible only in Bidirect mode)

Modem

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In Modem serial type, the device imitates a dial-up modem. Connections to TCP/IP networks can be established using AT commands. The connection can be initiated by a device connected via the RS232 serial interface with an ATD command: ATD <HOST>:<PORT>. If Direct connect settings are specified, the connection to the server is always active. Data mode can be entered by issuing the ATD command. Incoming connections are indicated by sending a RING to the serial interface.

The figure below is an example of available configuration fields for the Modem serial type and the table below provides information on these fields:

field name	value	description
Direct connect	ip:port | host:port; Default: none	Maintains a constant connection to the specified host. Leave empty if you are planning to use an ATD command to initiate the connection
TCP port	integer [0..65535]; Default: none	Internal TCP port number used to listen for incoming connections. Leave it empty to disable incoming connections
Initiation string*	string; Default: none	A command string that will be sent to the modem to initiate the connection in some particular way (optional)
No extra CR LF in response	yes | no; Default: no	Removes extra CR LF before response code; removes LF after response code

* This is the AT command set used in Modem mode of the serial interfaces:

command	description	usage
A	Answers an incoming call	To answer incoming connection: ATA
D	Dials a number	To initiate data connection: ATD <HOST>:<PORT> To enter data mode with Direct connect settings: ATD
E	Local echo	Turn local echo ON: ATE1 Turn local echo OFF: ATE0
H	Hang up current call	To end data connection: ATH
O	Return to data mode	To return to data mode from command mode: ATO
Z	Reset to default configuration	To reset the modem to default configuration: ATZ

Modbus gateway

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The Modbus gateway serial type allows redirecting TCP data coming to a specified port to the RTU specified by the Slave ID. The Slave ID can be specified by the user or be obtained directly from the Modbus header.

The figure below is an example of available configuration fields for the Modbus gateway serial type and the table below provides information on these fields:

field name	value	description
Listening IP	ip; Default: 0.0.0.0	IP address on which the Modbus gateway will wait for incoming connections
Port	integer [0..65535]; Default: 502	Port number used to listen for incoming connections
Slave ID configuration	User defined | Obtained from TCP; Default: User defined	Specifies whether slave IDs should be user defined or automatically obtained from TCP
Slave ID/Permitted slave IDs	integer | range of integers | multiple integers; Default: 1/1-247	Slave ID or range of permitted slave IDs. The way this field is named and its function depends on the value of the "Slave ID configuration" field. A range of IDs can be specified by placing a hyphen (-) between two integer numbers. For example, if you permit slave IDs in the range of 10 to 20, you would specify it as: 10-20 You can also specify multiple values that are not connected in a range using commas (,). For example, to specify 6, 50 and 100 as permitted slave IDs, you would have to use: 6,50,100

NTRIP client

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Networked Transport of RTCM via Internet Protocol (NTRIP) is a protocol for streaming differential GPS (DGPS) data over the Internet in accordance with specifications published by RTCM.

The figure below is an example of available configuration fields for the NTRIP client serial type and the table below provides information on these fields:

field name	value	description
IP address	ip; Default: 0.0.0.0	IP address of the NTRIP server
Port	integer; Default: none	TCP/UDP port used for communication with NTRIP server
Mount point	path to a file; Default: none	NTRIP mount point
Data format	NTRIP v2.0 TCP/IP | NTRIP v2.0 RSTP/RTP | NTRIP v1.0 | Automatic detection | NTRIP v2.0 UDP; Default: NTRIP v1.0	NTRIP version
User name	string; Default: none	User name used for NTRIP authentication
Password	string; Default: none	Password used for NTRIP authentication
Default NMEA string	string; Default: none	Optional NMEA string that will be used as the default value when initiating the connection to the NTRIP server (this value is only sent to the server if there is no NMEA from router's GPS device)