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Scilab Serial Communication Toolbox (SSCT)

Abstract:

Scilab Serial Communication Toolbox (SSCT) is inspired by a toolbox with a similar name originally developed by Aditya Sengupta and Enrico Segre. However, this new development line is an attempt to comply / resemble MATLAB serial communication functionalities and syntax as much as possible. The toolbox adds serial port (e.g., RS-232) protocol communication to Scilab / Scicoslab platforms, which are Free, Libre, and Open Source Software (FLOSS) alternatives of MATLAB. The toolbox can be used "for sending commands to control robots, motors, or reading sensors such as GPS, laser scanners, compasses, etc." [Esposito2009]. For the moment, the toolbox only works on Windows OS, but development for Linux and macOS are under progress and hopefully will be added in the future. This toolbox is still in the early-stage prototyping phase, and functions are not compiled. To use it, just download this Gist and run the ssctmain.sci in Scilab. For ScicosLab, due to the fact that multiline commenting /* …​ */ is yet to be implemented, the AsciiDoc documentations in those tags need to be removed in advance.

A serial object structure with similar properties / attributes and functions of the one in MATLAB has been developed. There are of course, some syntax differences due to Scilab intrinsic limitations, not-implemented features, as well as extra features considered to improve upon what MathWorks has already done. Considering that Scilab doesn’t have built-in Serial Port communication, external languages, including Tcl, PowerShell, CMD / batch, bash, C, C++, have been used. Moreover, due to the lack of object-oriented programing (OOP) capability in Scilab there are major differences between this toolbox and MATLAB. Mainly the serial object has no routine / subroutine / procedure accessible through the dot . operator, as seen in the OOP languages. Furthermore, all the MATLAB functions starting with an f are changed to s to avoid confusion and conflicts with other Scilab functions, as well as possible copyright issues. For example, MATLAB’s fopen is sopen in this toolbox. The syntax has been changed in a way to be more consistent and concise.

Although there are other FOSS options like Python, Octave, Julia, Sage, Maxima, R and FreeMat, …​, Scilab stands out among these options for having the great xcos / scicos environment, which is a replica of SIMULINK visual programing. xcos / scicos can also include code blocks from other languages such as C/C++, Fortran, Scilab, and Modelica language. In addition, Scilab / ScicosLab also have a nice GUI building functionality that resembles MATLAB syntax. In general for users coming from a MATLAB background, it is one of the best alternatives.

The codes / texts copied from other sources have the original licensing if not specified. The text of this author is under Creative Commons License BY-NC-SA, and the codes are GPLv3. The beautiful logo is designed by Alex Potterson. If you are a FLOSS developer and need a logo, you may contact him.

Introduction:

A typical serial port communication session has five steps:

1. Find the valid, available, open, defined serial ports using the slist function

2. Create a serial port object using the sdefine function, specifying the required properties.

3. Opening the port using the sopen function and adjusting the properties using sconfig and sinfo function

4. Sending or receiving data using

   1. sput and sputl for putting data to the serial port buffer and sflush for sending them out, or alternatively ssend/ssendl

   2. sget and sgetl function for taking data out of the serial port buffer

5. Closing the port using the sclose function and cleaning up the DefinedPorts list using the sdelete function.

Alternatively one can use the sprint/sprintl and sread/sreadl functions to send and read data in one step.

Example:

s1 = sdefine(Port = "COM1", BaudRate = 4800);
sopen(s1);
sput(s1, "*IDN?");
out = sget(s1);
sclose(s1);
sdelete(s1);
clear s1;

or alternatively using the simpler syntax:

sprint(Port = "COM1", Message = "*IDN?", BaudRate = 4800);
sread("COM1"); // to be implemented

serialobject.sci

Functions:

slist.sci

sdefine.sci

sopen.sci

sprint()

writes text to the serial devoice (similar to the MATLAB fprintf)

Syntax:

<Result> = sprint(<SerialPort => SerialPort, <Message => Message, <Mode = "syn"/"async">)

Description:

The SerialPort is a serial port object defined by the serial function or a string of a valid serial port such as COM1. The Message is a Scilab string which can be a formatted text created by Scilab’s msprintf function or a SCPI / SCI command known to the serial device.

Example:

sprint(s1, 'RS232?');

sprint(s1,'*IDN?');

sprint(s1, msprintf('%s','RS232?'));

sprint(s1, msprintf('ch:%d scale:%d', 1, 20e-3), 'sync');

sinfo()

Check the input and output buffer for available bytes and the status of the port

Syntax:

[InutBytesAvailable, <OutputBytesAvailable>, <Status>, <Result>] = sinfo(SerialPort)

Tutorials:

Example 01:

In this example (inspired by this tutorial) you will learn how to communicate with an Arduino microcontroller (MCU) expansion board and a Windows PC, through serial port. By the end of this example you will be able to read the value of a potentiometer, while this can be also expanded to reading any other sensors as well. To follow along the example you require the hardware including an Arduino Uno MCU development board, a potentiometer, wiring and breadboard.

Figure 1. An Ardunio Uno board with Potentiometer connected to port A0. (Image courtesy of arduino.cc)

Alternatively you can use SimulIDE to simulate the hardware and the Null-modem emulator (com0com) one Windows, to stablish a pair of virtual serial ports.

The Arduino code is:

int potPin = A0;

long val = 0;
long val_ = 0;

void setup() {
  Serial.begin(9600);
}

void loop() {

    val = ((long) analogRead(potPin));

    if (val != val_) {
      val_ = val;
      Serial.println(val);
    }

}

find the port connected to the Arduino board by running the command:

slist(Verbose = %t, PortList = "all")

This will show you are the serial ports recognized by the operating system, including the "available" and "open"`s. Under `Description you should be able to find the Arduino serial port.

Scilab code

ex01.sci

SimulIDE model

Click to see the source code

link:ex01.simu[role=include]

Result:

Figure 2. Live plotting of a potentiometer from Arduino

Nomenclature / Glossary:

For those who are not familiar with serial communication, some terms used in the practice can be difficult to grasp. In this section we will try to explain those terms.

• message: a serial message is 1 byte or 8 bits, which is able to represent between 0-255.

• terminator: indicates how a message should end. The common terminator is a carriage return indicated as "cr" in this toolbox.

• buffer: is like a container on the on both sides of the communication ports. The sender stores the data there before flushing them through the port and the receiver stores them there before dumping them over to the users space. The buffers have limited size which if exceeds the oldest data will be discarded. The size of buffer can be set through InputBufferSize and OutputBufferSize serial object property, which can not exceed the maximum provided by the hardware MaxInputBufferSize and MaxOutputBufferSize. If you do not flush/read the data on the sender/receiver side in time it can lead to irreversible data loss.

• checksum: in simple terms is basically a signature attached to each message, known by the receiver, which can be used to verify that the data is not garbled.

• polling and streaming: when requesting one single measurements from a sensor, it is called polling. If we read data from the sensor given a certain frequency it is called streaming.

• Serial Command Interface (SCI): firstly used by Motorola in the 1970s, is basically a language known by the serial device (e.g. MCU) to do certain things upon receiving certain messages.

• serial peripheral interface ( SPI )

• universal asynchronous receiver/transmitter (UART)

• USART

• Standard Commands for Programmable Instruments (SCPI)

• Transistor–transistor logic (TTL)

• TTY: teletypewriter, teletype, terminal

• Serial Port Profile (SPP)

Abbreviations:

• EIA Electronic Industries Alliance

• ANSI American National Standards Institute

• TIA Telecommunications Industry Association

• DIN Deutsches Institut für Normung

• RS Recommended Standard

  • 232

    • DTE Data Terminal Equipment eg. IBM computer, printer, plotter etc

    • DCE Data Communication/circuit-terminating Equipment eg. modem, multiplexors, etc

  • 422, 449, 485, 530

• ASCII: American Standard Code for Information Interchange

Pinout and Signals

Connectors used to be in the form of D-sub series or Mini-DIN

Serial and Parallel ports were found in two different forms, DB-25 and DE-9 (which is mistakenly also referred to as DB-9).

port (e.g. , DB-25, DE-9 …​),voltage (TTL 5V, True RS-232 12V), communication standards (RS-232, USB), data transmission method (parallel or serial)

DE-9	DB-25	acronym / abbreviation	Name	typical purpose	DTE	DCE
1	8	DCD	Data Carrier Detect	DCE is receiving a carrier from a remote DCE	in	out
2	3	RxD	Received Data	Carries data from DCE to DTE	in	out
3	2	TxD	Transmit Data	Carries data from DTE to DCE	out	in
4	20	DTR	Data Terminal Ready	DTE is ready to receive, initiate, or continue a call	out	in
5	7	GND	Common Ground	Zero voltage reference (signal ground)	-	-
6	6	DSR	Data Set Ready	DCE is ready to receive and send data	in	out
7	4	RTR	Ready To Receive	DTE is ready to receive data from DCE	out	in
7	4	RTS	Request To Send	flow control, DTE requests the DCE prepare to transmit data	out	in
8	5	CTS	Clear To Send	DCE is ready to accept data from the DTE	in	out
9	22	RI	Ring Indicator	DCE has detected an incoming ring signal on the telephone line	in	out
	1	PG	Protective Ground	Frame / Chassis Ground	-	-
	9
	10
	11
	12	SDCD	Secondary Carrier Detect	Tone from a modem	in	out
	13	SCTS	Secondary Clear To Send		in	out
	14	STD	Secondary Transmitted Data		out	in
	15	ST	Send Timing
	16	SRD	Secondary Received Data		in	out
	17	RT	receive timing
	18			Loopback
	19	SRTS	Secondary Request To Send		out	in
	21			Loopback
	23			Signal rate selection
	24	TT	Transmitter Timing
	25

References

• [Esposito2009] Joel M. Esposito, Tutorial: Serial Communication in Matlab, 2009, URL