Libelium RS-232 User Manual
RS-232 Module
Communication Guide
Document version: v7.1 - 02/2017
© Libelium Comunicaciones Distribuidas S.L.
INDEX
1. Introduction ......................................................................................................................................... 4
1.1. The standard ..................................................................................................................................................................................4
2. Hardware ............................................................................................................................................. 6
2.1. Electrical features .........................................................................................................................................................................6
2.2. Connection diagram ...................................................................................................................................................................6
2.3. Consumption .................................................................................................................................................................................8
2.4. Connector .......................................................................................................................................................................................8
3. Dual radio with Expansion Board ..................................................................................................... 10
3.1. Expansion Radio Board ........................................................................................................................................................... 10
Index
4. RS-232 on Plug & Sense! ................................................................................................................... 12
5. Applications ....................................................................................................................................... 14
6. Libelium’s library ............................................................................................................................... 16
7. Library functions ............................................................................................................................... 17
7.1. Library constructor ................................................................................................................................................................... 17
7.2. Switching the module on .......................................................................................................................................................17
7.3. Switching the module o ......................................................................................................................................................17
7.4. Conguring communication speed ................................................................................................................................... 18
7.5. Conguring the number of stop bits ................................................................................................................................. 18
7.6. Conguring the parity bit ...................................................................................................................................................... 19
7.7. Sending data...............................................................................................................................................................................20
7.7.1. Sending a char ............................................................................................................................................................20
7.7.2. Sending an integer ...................................................................................................................................................20
7.7.3. Sending a string .........................................................................................................................................................20
7.7.4. Sending with base .....................................................................................................................................................21
7.7.5. Sending a long ............................................................................................................................................................21
7.8. Receiving data ............................................................................................................................................................................ 22
7.9. Knowing when new data is available ................................................................................................................................23
7.10. Flushing buer ........................................................................................................................................................................23
8. Certications ...................................................................................................................................... 24
9. Code examples and extended information ..................................................................................... 25
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Index
10. API changelog .................................................................................................................................. 27
11. Documentation changelog ............................................................................................................. 28
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Introduction
1. Introduction
This guide explains the RS-232/Modbus module features and functions. This product was designed for Waspmote v12 and
continues with no changes for Waspmote v15. There are no great variations in this library for our new product line Waspmote
v15, released on October 2016.
Anyway, if you are using previous versions of our products, please use the corresponding guides, available on our Development
website.
You can get more information about the generation change on the document “New generation of Libelium product lines”.
1.1. The standard
The RS-232 standard was rst introduced in 1962 by the Radio Sector of the EIA. The original DTEs (data terminal equipment)
were electromechanical teletypewriters, and the original DCEs (data circuit-terminating equipment) were usually modems.
When electronic terminals began to be used, they were often designed to be interchangeable with teletypewriters, and so
supported RS-232. The C revision of the standard was issued in 1969 in part to accommodate the electrical characteristics of
these devices. For many years, an RS-232-compatible port was a standard feature for serial communications, such as modem
connections, on many computers. The RS-232 standard is still used to connect industrial equipment (such as PLCs), console
ports and special purpose equipment.
The IEEE RS-232 standard denes electrical, signal timing, and size connectors. Use of a common ground, limits RS-232 to
applications with relatively short cables. RS-232 connection consisting only of transmit data, receive data, and ground. RS-232
protocol uses bipolar signal. Valid signals are ±3 to +15 volts, the ±3V range is not a valid RS-232 level. Data signals between -3V
and -15V represents a logic 1. The logic 0 is represented by a voltage of between +3 V and +15 V.
Figure : RS-232 voltage conversion
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Introduction
Serial transmission requires synchronization. A logic 0 is sent as a start bit for the synchronization, followed by normally eight
bits. After the data itself, a parity bit is sent. It is optional and it can be chosen to have even or odd parity. Finally a stop bit is sent.
This is normally one bit long and is used to signify the end of a particular byte. Sometimes two stop bits are required. This is an
option that can be set on some equipments.
This list includes some of the more common uses of the standard:
• Dial-up modems
• GPS receivers (typically NMEA 0183 at 4,800 bit/s)
• Bar code scanners and other point of sale devices
• LED and LCD text displays
• Satellite phones, low-speed satellite modems and other satellite based transceiver devices
• Flat-screen (LCD and Plasma) monitors to control screen functions by external computer, other AV
• components or remotes
• Test and measuring equipment such as digital multimeters and weighing systems
• Updating Firmware on various consumer devices
• Some CNC controllers
• Uninterruptible power supply
• Stenography or Stenotype machines
• Software debuggers that run on a 2nd computer
• Industrial eld buses
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Hardware
2. Hardware
The RS-232 / Modbus module has been tested with various devices and is compatible with the majority of commercial modules,
but this does not ensure the working with all of them. Be sure that the RS-232 module ts your technical requirements. The nal
user is the responsable to perform the task of communicatiing the RS-232 module with other commercial devices.
2.1. Electrical features
• Board power voltages: 3.3 V
• Maximum admitted voltage: -0.3 V to +6 V
• Typical data rate: 115200 bps
• Temperature range: [ 0 °C, 70 °C ]
• Dimensions: 33 x 31.5 mm
2.2. Connection diagram
The RS-232 Serial / Modbus module uses the UART pins, RX and TX, for communication. The Expansion Board allows to connect
two boards at the same time in the Waspmote sensor platform. This means a lot of dierent combinations are possible using
any of the radios available for Waspmote (802.15.4, ZigBee, DigiMesh, 868 MHz, 900 MHz, LoRa, WiFi, GPRS, GPRS+GPS, 3G, 4G,
Sigfox, LoRaWAN, Bluetooth Pro, Bluetooth Low Energy and RFID/NFC) and the RS-232 module.
In the next photo you can see the available sockets along with the UART assigned. The RS-232 module can be connected
normally on socket 0, and in socket 1 with the Expansion Board.
Figure : RS-232 in socket0
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Hardware
Figure : RS-232 in socket1
The RS-232 Serial / Modbus module can be used with two dierent protocols:
• 1. RS-232 Serial standard (this is the scope of this guide)
• 2. Modbus protocol (which adds some features; see the Modbus Communication Guide for more details)
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Hardware
2.3. Consumption
RS-232 module uses a low power transceiver. The board is guaranteed to run at data rates of 120 kbps while maintaining RS-232
output levels. The next table shows the consumption at various baud rates.
Baud rate (bps) Consumption (mA)
300 1,65
600 1,65
1200 1,65
2400 1,67
4800 1,67
9600 1,72
19200 1,8
38400 1,9
57600 2,0
115200 2,26
Figure : RS-232 consumption table
2.4. Connector
The standard recommends but does not make mandatory the D25-pin connector. In the RS-232 module, the connector is a
DB9 female. The RS-232 module uses pin 2 to receive data, 3 to transmit and ground pin. The DB9 connector is used in many
applications; for example, any PC has a serial DB9 connector. It provides size and cost benets. Also the RS-232 9-pin conguration
is sucient in most circumstances, because many of the lines available for RS-232 signaling are rarely used. This means that the
DB9 connector is able to provide all the required connectivity for most applications.
Figure : DB9 connector
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Hardware
The RS-232 module comes with a standard male-female DB9 cable. This cable is useful for connecting the module to other RS232 devices which have a DB9 male connector.
Figure : Male-female DB9 cable
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