TRB142 RS232

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Summary[edit | edit source]

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[edit | edit source]

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

RS232 connector pinout
Trb142 rs232 pinout v3.png
Pin Name Description
2 RXD Output
3 TXD Input
5 GND -
7 RTS Input
8 CTS Output

Cables[edit | edit source]

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.


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

Services rs232 connector female male.PNG

See straight cable pinout below:

Straight cable pinout v2.png


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

Male male rs232 cable.jpg

See straight crossed cable pinout below:

Straight crossed rs232 cable pinout v2.png


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[edit | edit source]

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:

Trb142 webui services rs232 rs232 configuration general v1.png

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[edit | edit source]

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[edit | edit source]


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[edit | edit source]


In Over IP serial type the device provides a connection to a TPC/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:

Trb142 webui services rs232 rs232 configuration serial type over ip v4.png

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[edit | edit source]


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:

Trb142 webui services rs232 rs232 configuration serial type modem v1.png

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[edit | edit source]


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:

Trb142 webui services rs232 rs232 configuration serial type modbus gateway v1.png

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[edit | edit source]


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:

Trb142 webui services rs232 rs232 configuration serial type ntrip client v1.png

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)