CERTIFICATION
This is to certify that this seminar work was done by OSISIOGU, UKACHI OLUWASEUN OLUWASEUN of the department department of Electronic and Computer Computer Engineering in partial partial fulfillment for the award of Bachelor Degree in Engineering at Nnamdi Azikiwe University, Awka
------------------------------------Prof. (Mrs.) C. C. Okezie Project Project Supervisor Supervisor
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DEDICATION I dedicate dedicate this this seminar seminar paper to the Almigh Almighty ty God for for His grace grace and and infinite infinite love love towar towards ds me me and and to my darl darlin ing g pare parent nts, s, sib sibli ling ngs, s, and and clos closee frie friend ndss for for thei theirr encouragem encouragement ent morally morally,, academically academically,, financially financially and otherwise. otherwise.
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ACKNOWLEDGEMENT I thank God for the grace of life and abundance of blessings which He showered upon me. me. I wish wish to expres expresss my gratitude gratitude to my my supervi supervisor sor Prof (Mrs.) (Mrs.) C.C. Okezie Okezie for her support, guidance and encouragement during this seminar writing. I also want to acknowledge my parents, Prof. and Mrs. U. A. Osisiogu, who has been of immense supports supports to my academics and my siblings Onyekachi, Tochukwu Tochukwu and Ayo-Oluw Ayo-Oluwaa who have have been a source source of encouragem encouragement. ent. I also express express my gratitude gratitude to Prof. Prof. V.E Idigio, Idigio, Prof. Iyiama, Iyiama, Dr. A.C.O A.C.O Azugbogu, Azugbogu, Dr. Ohaneme, Dr. (Mrs.) S.U. Nnebe, Dr. Ken Akpado, Dr. Tony Isizoh. Dr. T.L Alumuna, Dr. Ifeagwu, , Dr. Udenze, Engr. Steve Ufuorah, Engr. Ezeagu, Engr. Azubik Azubikee Aniedu, Aniedu, Engr Engr.. Okorogu Okorogu and Gerald Gerald Nwalo Nwalozie zie.. These These ones ones have impacte impacted da lot of knowl knowledge edge in me turning turning me me into the the well-equi well-equipped pped man man that I am today. today. I know that the sky is their limit limit and they will achieve much more in their lives. Last but not the least are my wonderful friends, Onyedika, Onyedika, Confidence, Confidence, Jason, Jason, Uzoma, Henry, Henry, Kelechi, Gabriel and a host of others who in one one way or the other other made a huge impact in my life, I love you all.
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TABLE OF CONTENTS
CERTIFICATION....................................... CERTIFICATION............................... .................... ....................... .................... .................... .............. ... 1 DEDICATION ...................... ................................ ...................... ....................... .................... .................... ....................... ................ .... 2 ACKNOWLEDGEMENT ...................... ................................ .................... ...................... ...................... .................. ........3 3 TABLE OF CONTENTS ...................... ................................ ..................... ...................... ..................... .................... ..........4 4 SECTION ONE........... ONE ....................... ..................... .................... ...................... ..................... .................... ...................... ................ .... 7 INTRODUCTION ....................... ................................ .................... ....................... ..................... .................... ..................... ..........7 7 SECTION TWO: AN AN OVERVIEW ON ARDUINO ....................... ........................... .... 10 2.1 Introductio Introduction n ........................... ............................................ .............................. .............................. .............................. .................. ..... 10 2.2
Arduino Arduino Uno........................ Uno......................................... .............................. .............................. ............................... .................. .... 11
2.3 General General Specificat Specifications ions .......................... ........................................... .............................. .............................. .................... ... 11 2.3.1 Power Specificatio Specification.............................. n.......................................................................................12 .........................................................12 2.3.2 Memory Memory Specificati Specification on...................................................... ...................................................................................13 .............................13 2.3.3 Input and Output..........................................................................................13 2.3.4
Communicatio Communication n ........................................................ .........................................................................................14 .................................14
2.4
Programmi Programming ng the Arduino........................ Arduino......................................... .............................. ......................... ............ 15
2.5
Automatic Automatic (Software) (Software) Reset .......................... ........................................... ............................... ..................... ....... 16
2.6
USB Over-c Over-current urrent Protection Protection .......................... ........................................... .............................. .................. ..... 16
2.7
Physical Physical Characte Characteristic risticss .................. ................................... ............................... ........................... ..................... ........ 17
3.
SECTION SECTION THREE: THREE: SERIAL COMMUNICATION COMMUNICATION ........ ............ ........ ...... .. 18
3.1
Definition Definition............. .......................... .............................. ............................... .............................. .............................. ..................... ....... 18
3.2
Differences Differences between between Serial Serial and Parallel Parallel Commu Communicat nication ion ................. ................. 18
3.3
Clock skew........................... skew............................................ .............................. .............................. .............................. .................. ..... 20
3.4
Asynchronous Asynchronous and Synchronous Synchronous Data Transmission Transmission ........................ ........................ 21 4
3.4.1 The advantages and disadvantages of synchronous over asynchronous serial communication............................................................................................23
3.5
The DCE and the DTE ........................................................................ 23
3.6
The Mode of Operation of a Serial Rate Transfer (SRT)............... 24
3.6.1
Baud rate ...................................................................................................26
3.6.2
Data bits ....................................................................................................27
3.6.3
Start and Stop (Synchronisation) bits:.....................................................27
3.6.4 Parity .............................................................................................................28
3.7
Examples of Serial Communication Standards............................... 29
3.7.1
RS-232........................................................................................................29
3.7.2 RS-422................................................................................................ 30 3.7.3 RS-423................................................................................................ 31 3.7.4 RS-485................................................................................................ 31 3.7.5 USB (Universal Serial Bus)............................................................... 33 3.7.6 Fire Wire (IEEE 1394)..................................................................................35 3.7.7 Ethernet.........................................................................................................35 3.7.8
MIDI...........................................................................................................36 2
3.7.9 IIC or I C- Inter-Integrated Circuit ............................................................37 3.7.10 SPI-Serial Peripheral Interface..................................................................38 3.7.11 PCI Express.................................................................................................39
SECTION FOUR .....................................................................................41 4.1 THE PROCEDURE FOR SERIAL COMMUNICATION IN ARDUINO IN CREATING SYSTEMS ...................................................... 41 4.2
UART.................................................................................................... 42 5
4.3 Applications of Serial Communication in Arduino .............................. 42 4.4
Examples of the utilisation of serial communication in Arduino ... 43
4.4.1
Sending Debug Information from Arduino to Computer .......................43
4.4.2
Sending Formatted Text and Numeric Data from Arduino....................43
4.4.3 Receiving serial Data in Arduino .................................................................44 4.4.4 Arduino to Arduino communication............................................................44
SECTION FIVE: CONCLUSION ......................................................... 45 REFERENCES ........................................................................................ 46
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SECTION ONE INTRODUCTION In the field of electronics, the interconnection of circuits in order to create a symbiotic system is vital. For this interconnection to be accomplished, between processors, sensors and other integrated circuits they must share a common communication protocol. One of such communication protocol is the serial communication protocol. The aim of this paper is to present a good understanding of serial communication and how it relates to Arduino. Serial in a general context means one after the other, although in the context of computing it means the sending of computer information sequentially
[1]
.
Communication simply means the exchange of information between people and devices.
[2]
Therefore serial communication can be defined as the form of information
exchange in which the individual bits that compromise the information in the form of bytes or character travel one after the other through a single channel. However, serial communication is common method of transmitting data between a computer and a peripheral device such as a programmable instrument or even another computer.
[3]
Serial communication transmits data one bit at a time,
sequentially, over a single communication line to a receiver. Serial is also a most popular communication protocol that is used by many devices for instrumentation. The history of long distance communication can be traced back to the days when smoke signaling where by covering a fire with blanket and quickly removing it can a generate a puff of smoke. With some training, the sizes, shapes and timing of these puffs can be observed from a long distance, noticeable to anyone within its visual range. Stone bowls used by Native Americans and the towers of the Great Wall of China are examples of signaling stations that utilized this form of communication. th
As technology advanced; in the 19 century the Morse code was invented by Samuel F.B. Morse, the use of telegraph was introduced concurrently and long distanced 7
communication improved to an extent. In 1960 work on ASCII (American Standard Code for Information Interchange) began and the first edition of the standard was published in 1963, a major revision in 1967, and the most recent update in 1986.
[4]
Till today it defines codes for the 128 characters used in communication. In 1962 the first serial port communication was introduced by the Radio Sector of the EIA. This particular technology has evolved into various standards like the USB, FireWire, 2
Ethernet, RS-485, SPI, SONET and I C with many others. The evolution that occurred in serial communication can be said to have come because of the insatiable need for people to communicate faster and even over longer distances. Serial communication can now be used to transfer data with a very high throughput. There are still recent developments that are in progress on how to even increase the throughput at even longer distances which makes this subject an interesting and important field of research. Arduino is an open-source computer hardware and software company, project and user community that designs and manufactures kits for building digital devices and interactive objects that can sense and control the physical world.
[5]
The Arduino platform has become quite popular with people just starting out with electronics, and for good reason. Unlike most previous programmable circuit boards, the Arduino does not need a separate piece of hardware (called a programmer) in order to load new code onto the board, a USB can be simply used. Additionally, the Arduino IDE uses a simplified version of C++, making it easier to learn to program. Finally, Arduino provides a standard form factor that breaks out the functions of the microcontroller into a more accessible package. The importance of this paper is to look at this vital protocol (serial communication) and understand how it works with Arduino by understanding Arduino Uno and how serial communication works conventionally. Once the foundation has been laid, this paper will then connect these two concepts in order to give a satisfactory understanding on the topic. 8
Section 1 gives a general overview and some basic definitions on the subject matter. Section 2 gives a detailed view on Arduino. Section 3 deals with some necessary details on serial communication and gives an explanation some serial communication standards. Section 4 deals with how Arduino utilises the capacity of serial communication and Section 5 gives the summary this paper.
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SECTION TWO: AN OVERVIEW ON ARDUINO 2.1 Introduction Arduino is an open-source platform used for building electronics projects. Arduino consists of both a physical programmable circuit board (often referred to as a microcontroller) and a piece of software, or IDE (Integrated Development Environment) that runs on the users computer, used to write and upload computer code to the physical board. The Arduino platform has become quite popular with people just starting out with electronics, and for good reason. Unlike most previous programmable circuit boards, the Arduino does not need a separate piece of hardware (called a programmer) in order to load new code onto the board; the user can simply use a USB cable. Additionally, the Arduino IDE uses a simplified version of C++, making it easier to learn to program. Finally, Arduino provides a standard form factor that breaks out the functions of the microcontroller into a more accessible package. Arduino manufactures many different boards, each with different potentials. In addition, Arduino is “open source” hardware. This implies that others can modify and produce derivatives of Arduino boards that provide even more functionality. Examples such boards are: a) Arduino Uno b) LilyPad Arduino c) RedBoard d) Arduino Mega e) Arduino Leonardo This paper will only discuss Arduino Uno and its specifications
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2.2
Arduino Uno
The Arduino Uno is a microcontroller board based on the ATmega328 (datasheet). It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with an AC-to-DC adapter or battery to get started. The Uno differs from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega8U2 programmed as a USB-to-serial converter. "Uno" means one in Italian and is named to mark the upcoming release of Arduino 1.0. The Uno and version 1.0 will be the reference versions of Arduino, moving forward. The Uno is the latest in a series of USB Arduino boards, and the reference model for the Arduino platform.
[6]
2.3 General Specifications
Microcontroller
ATmega328
Operating Voltage
5V
Input Voltage (recommended)
7-12V
Input Voltage (limits)
6-20V
Digital I/O Pins
14 (of which 6 provide PWM output)
Analog Input Pins
6
DC Current per I/O Pin
40 mA
DC Current for 3.3V Pin
50 mA
SRAM
2 KB
EEPROM
1 KB
Clock Speed
16 MHz
Table 1: Arduino Uno Specifications 11
Figure 1: A Diagram of an Arduino Uno Board
2.3.1 Power Specification The Arduino Uno can be powered via the USB connection or with an external power
supply. The power source is selected automatically. External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack. Leads from a battery can be inserted in the GND and VIN pin headers of the POWER connector. The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.
The power pins are as follows: 12
A) VIN The input voltage to the Arduino board when it's using an external power ource (as opposed to 5 volts from the USB connection or other regulated power source). The user can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin.
B) 5 V The regulated power supply used to power the microcontroller and other components on the board. This can come either from VIN via an on-board regulator, or be supplied by USB or another regulated 5V supply.
C) 3.3V A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
D) GND. Ground pins. E) IOREF: This pin on the Arduino board provides the voltage reference with which the microcontroller operates. A properly configured shield can read the IOREF pin voltage and select the appropriate power source or enable voltage translators on the outputs for working with the 5V or 3.3V. 2.3.2 Memory Specification The ATmega328 has 32 KB (with 0.5 KB used for the bootloader). It also has 2 KB
of SRAM and 1 KB of EEPROM. 2.3.3 Input and Output Each of the 14 digital pins on the Uno can be used as an input or output, using
pinMode(), digitalWrite(), and digitalRead() functions. They operate at 5 volts. Each pin can provide or receive a maximum of 40 mA and has an internal pull-up resistor (disconnected by default) of 20-50 kOhms. In addition, some pins have specialized functions: 13
Serial: 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL serial data.
These pins are connected to the corresponding pins of the ATmega8U2 USB-to-TTL Serial chip. External Interrupts: 2 and 3. These pins can be configured to trigger an interrupt
on a low value, a rising or falling edge, or a change in value. See the attachInterrupt() function for details. PWM: 3, 5, 6, 9, 10, and 11. Provide 8-bit PWM output with the analogWrite()
function. SPI: 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins support SPI
communication using the SPI library. LED 13: There is a built-in LED connected to digital pin 13. When the pin is HIGH
value, the LED is on, when the pin is LOW, it's off. The Uno has 6 analog inputs, labeled A0 through A5, each of which provide 10 bits of resolution (i.e. 1024 different values). By default they measure from ground to 5 volts, though is it possible to change the upper end of their range using the AREF pin and the analogReference() function. Additionally, some pins have specialized functionality: TWI: A4 or SDA pin and A5 or SCL pin. Support TWI communication using the
Wire library. There are a couple of other pins on the board: AREF: Reference voltage for the analog inputs. Used with analogReference(). Reset. Bring this line LOW to reset the microcontroller. Typically, this is used to
add a reset button to shields which block the one on the board. 2.3.4 Communication The Arduino Uno has a number of facilities for communicating with a computer,
another Arduino, or other microcontrollers. The ATmega328 provides UART-TTL (5V) serial communication, which is available on digital pins 0 (RX) and 1 (TX). An ATmega8U2 on the board channels this serial communication over USB and appears as a virtual com port to software on the computer. The '8U2 firmware uses the
14
standard USB COM drivers, and no external driver is needed. However, on Windows, an *.inf file is required. The Arduino software includes a serial monitor which allows simple textual data to be sent to and from the Arduino board. The RX and TX LEDs on the board will flash when data is being transmitted via the USB-to serial chip and USB connection to the computer (but not for serial communication on pins 0 and 1). A SoftwareSerial library allows for serial communication on any of the Uno's digital pins. The 2
ATmega328 also support I C (TWI) and SPI communication. The Arduino software 2
includes a Wire library to simplify use of the I C bus.
2.4
Programming the Arduino
The Arduino Uno can be programmed with the Arduino software .Select “Arduino Uno” from the Tools > Board menu (according to the microcontroller on the board). The ATmega328 on the Arduino Uno comes pre-burned with a boot loader that allows the user to upload new code to it without the use of an external hardware programmer. It communicates using the original STK500 protocol (reference, C header files). The user can also bypass the boot loader and program the microcontroller through the ICSP (In-Circuit Serial Programming) header. The ATmega16U2 (or 8U2 in the rev1 and rev2 boards) firmware source code is available. The ATmega16U2/8U2 is loaded with a DFU boot loader, which can be activated by: On Rev1 boards: connecting the solder jumper on the back of the board (near the
map of Italy) and then resetting the 8U2. On Rev2 or later boards: there is a resistor that pulling the 8U2/16U2 HWB line to
ground, making it easier to put into DFU mode. The user can then use Atmel's FLIP software (Windows) or the DFU programmer (Mac OS X and Linux) to load a new firmware. Or the user can use the ISP header with an external programmer (overwriting the DFU boot loader). 15
2.5
Automatic (Software) Reset
Rather than requiring a physical press of the reset button before an upload, the Arduino Uno is designed in a way that allows it to be reset by software running on a connected computer. One of the hardware flow control lines (DTR) of the ATmega8U2/16U2 is connected to the reset line of the ATmega328 via a 100 Nano farad capacitor. When this line is asserted (taken low), the reset line drops long enough to reset the chip. The Arduino software uses this capability to allow you to upload code by simply pressing the upload button in the Arduino environment. This means that the boot loader can have a shorter timeout, as the lowering of DTR can be well coordinated with the start of the upload. This setup has other implications. When the Uno is connected to either a computer running Mac OS X or Linux, it resets each time a connection is made to it from software (via USB). For the following half-second or so, the boot loader is running on the Uno. While it is programmed to ignore malformed data (i.e. anything besides an upload of new code), it will intercept the first few bytes of data sent to the board after a connection is opened. If a sketch running on the board receives one-time configuration or other data when it first starts, make sure that the software with which it communicates waits a second after opening the connection and before sending this data. The Uno contains a trace that can be cut to disable the auto-reset. The pads on either side of the trace can be soldered together to re-enable it. It's labeled "RESET-EN". You may also be able to disable the auto-reset by connecting a 110 ohm resistor from 5V to the reset line.
2.6
USB Over-current Protection
The Arduino Uno has a resettable poly-fuse that protects your computer's USB ports from shorts and over-current. Although most computers provide their own internal protection, the fuse provides an extra layer of protection. If more than 500 mA is
16
applied to the USB port, the fuse will automatically break the connection until the short or overload is removed.
2.7
Physical Characteristics
The maximum length and width of the Uno PCB are 2.7 and 2.1 inches respectively, with the USB connector and power jack extending beyond the former dimension. Three screw holes allow the board to be attached to a surface or case. Note that the distance between digital pins 7 and 8 is 160 mil not an even multiple of the 100 mil spacing of the other pins.
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3. 3.1
SECTION THREE: SERIAL COMMUNICATION
Definition
Serial communication is a common method of transmitting data between a computer and a peripheral device such as a programmable instrument or even another computer. Serial communication transmits data one bit at a time, sequentially, over a single communication line to a receiver. Serial is also a most popular communication protocol that is used by many devices for instrumentation. [7] This method is used when data transfer rates are very low or the data must be transferred over long distances and also where the cost of cable and synchronization difficulties, make parallel communication impractical. Serial communication is popular because most computers have one or more serial ports, so no extra hardware is needed other than a cable to connect the instrument to the computer or two computers together.
3.2
Differences between Serial and Parallel Communication
In this section, a comparative study on parallel and serial communications will be treated in order to aid the understanding of the differences, advantages and disadvantages of both in detail. Parallel ports are typically used to connect a PC to a printer and are rarely used for other connections. A parallel port sends and receives data eight bits at a time over eight separate wires or lines. This allows data to be transferred very quickly. However, the setup looks more bulky because of the number of individual wires it must contain. But, in the case of a serial communication, as stated earlier, a serial port sends and receives data, one bit at a time over one wire. While it takes eight times as long to transfer each byte of data this way, only a few wires are required. Although this is slower than parallel communication, which allows the transmission of an entire byte at once, it is simpler and can be used over longer distances. For example, the IEEE 488 specifications for parallel communication state that the cabling between equipment can be no more than 20 meters total, with no more than 2 18
meters between any two devices; serial, however, can extend as much as 1200 meters (with high-quality cable). However, at first sight it would seem that a serial link must be inferior to a parallel one, because it can transmit less data on each clock tick. Although, it is often the case that, in modern technology, serial links can be clocked considerably faster than parallel links, and achieve a higher data rate. Even in shorter distance communications, serial computer buses are becoming more common because of a tipping point where the disadvantages of parallel busses (clock skew, interconnect density) outweigh their advantage of simplicity (no need for serializer and deserializer). The serial port on a PC is a full-duplex device meaning that it can send and receive data at the same time. In order to be able to do this, it uses separate lines for transmitting and receiving data. From the above discussion we could understand that serial communications have many advantages over parallel communication like: a) Requires fewer interconnecting cables and hence occupies less space. b) "Cross talk" is less of an issue, because there are fewer conductors compared to that of parallel communication cables. c) Many ICs and peripheral devices have serial interfaces. d) Clock skew between different channels is not an issue. e) No need of Serialiser/Deserialiser (SerDes). f) Cheaper to implement.
Figure 3: Serial Communication
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Figure 2: Parallel Communication
In the attempt to gain a good understanding of serial communication it is vital that the following terms are explained.
3.3
Clock skew
Clock skew is a phenomenon in synchronous circuits in which the clock signal sent from the clock circuit arrives at different components at different times, which can be caused by many things, like: a) Wire-interconnect length, b) Temperature variations, c) Variation in intermediate devices, d) Capacitive coupling, e) Material imperfections, As the clock rate of a circuit increases, timing becomes more critical and less variation can be tolerated if the circuit is to function properly. There are two types of clock skew: Positive skew, which occurs when the clock reaches the receiving register later than it reaches the register sending data to the receiving register and negative skew which just opposite: the receiving register gets the clock earlier than
the sending register. Two types of violation can be caused by clock skew. One problem is caused when the clock travels more slowly than the path from one register to another - allowing data to penetrate two registers in the same clock pulse, or maybe destroying the integrity of the latched data. This is called a hold violation because the previous data is not held long enough at the destination flip-flop to be properly
clocked
20
through.
3.4 Asynchronous and Synchronous Data Transmission Like any data transfer methods, Serial Communication also requires coordination between the sender and receiver. For example, when to start the transmission and when to end it, when one particular bit or byte ends and another begins, when the receiver's capacity has been exceeded, and so on. Here comes the need for synchronization between the sender and the receiver. A protocol defines the specific methods
of
coordinating
transmission
between
a
sender
and
receiver.
Let us take an example. A serial data signal between two PCs must have individual bits and bytes that the receiving PC can distinguish. If it does not, then the receiving PC cannot tell where one byte ends and the next one begin or where one bit ends and begins. So the signal must be synchronized in such a way that the receiver can distinguish the bits and bytes as the transmitter intends them to be distinguished. There are two ways to synchronize the two ends of the communication namely synchronous and asynchronous. The synchronous signaling methods use two
different signals. A pulse on one signal line indicates when another bit of information is ready on the other signal line. The asynchronous signaling methods use only one signal. The receiver uses transitions on that signal to figure out the transmitter bit rate (known as auto baud) and timing, and set a local clock to the proper timing, typically using a PLL to synchronize with the transmission rate. A pulse from the local clock indicates when another bit is ready. That means synchronous transmissions use an external clock, while asynchronous transmissions are use special signals along the transmission medium. (Refer to Figure 4) Asynchronous communication is the commonly prevailing communication method in the personal computer industry, due to the reason that it is easier to implement and has the unique advantage that bytes can be sent whenever they are ready, and no need to wait for blocks of data to accumulate.
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Figure 4: (1) Synchronous and (2) Asynchronous serial Communication.
22
3.4.1 The advantages and disadvantages of synchronous over serial communication •
asynchronous
The one of the crucial advantages of synchronous data transfer is the lower overhead and thus, greater throughput, compared to asynchronous one. But it has some disadvantages such as,
•
Slightly more complex and
•
Hardware is more expensive. One of the main disadvantages of asynchronous technique is the large relative overhead, where a high proportion of the transmitted bits are uniquely for control purposes and thus carry no useful information. But it holds some advantages like, 1) Simple and doesn't require much synchronization on both communication sides. 2) The timing is not as critical as for synchronous transmission; therefore hardware can be made cheaper. 3) Set-up is very fast, so well suited for applications where messages are generated at irregular intervals, for example data entry from the keyboard.
3.5
The DCE and the DTE
The terms DTE and DCE are very common in the data communications technologies. DTE is an acronym for Data Terminal Equipment and DCE stands for Data Communications Equipment . As the full DTE name indicates, this is a piece of
device that ends a communication line, whereas the DCE provides a path for communication. Using the following example a good understanding of their functions can be achieved. For instance, a computer which wants to communicate 23
with the Internet through a modem and a dial-up connection, in order to get to the Internet the computer tells the modem to dial the number of the internet service provider. After the modems have dialed the number, the modem of the provider will answer the call. Then your connection is established. Now you have a connection with the server from your provider and you can use the Internet. In this example, your PC is a Data Terminal (DTE). The two modems (internal modem and that one of the provider's) are DCEs. They make the communication between you and your provider possible. When there is a need to look at the server of your provider, do we call that a DTE or DCE? The answer is a DTE. It ends the communication line between you and the server, although it gives you the possibility to surf around the globe. The reason why it is a DTE is that when you want to go from your provider's server to another place it uses another interface. So DTE and DCE are interface dependent devices. It means, for your connection to the server, the server is a DTE, but the same server is a DCE for the equipment that it is attached to the rest of the Network.
3.6 The Mode of Operation of a Serial Rate Transfer (SRT) Serial communication requires the specification the following five parameters: 1) The speed or baud rate of the transmission, 2) The number of data bits encoding a character, 3) The sense of the optional parity bit, (whether to be used or not, if yes then odd or even) 4) The number of stop bits, 5) Full or half-duplex operation.
24
Each transmitted character is packaged in a character frame that consists of a single start bit followed by the data bits, the optional parity bit, and the stop bit or bits, as shown in the Figure 4 After the stop bit, the line may remain idle indefinitely, or another character may immediately be started. The minimum stop bit length required by the system can be larger than a "bit". In fact it can be 1.5 stop bits, or 2 stop bits, or even the new hardware that doesn't support fractional stop bits can be configured to send 2 stop bits when transmitting and requiring 1 stop bit when receiving.
Figure 5: Diagram of a Character Frame
Typically, serial communication is carried out using ASCII form of the data. Communication is completed using 3 transmission lines: Ground, Transmit, and Receive. Since serial is asynchronous (in many applications), the port is able to transmit data on one line while receiving data on another. Other lines are available for handshaking, but are not required. The important serial characteristics are baud rate, data bits, stop bits, and parity and for two ports to communicate, these
parameters must match. In the following section the parameters that are common with serial communication will be explained.
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3.6.1 Baud rate
The baud rate is used to specify data speed, which is a measure of the number of times a digital signal changes state in one second or the number of signal events or signal transitions occurring per second. The changes can be a) From positive voltage to zero voltage, b) From zero voltage to negative voltage, or c) From positive voltage to negative voltage. The baud rate can never be higher than the raw bandwidth of the channel, as measured in Hz. Baud rate and bit rate, often and incorrectly, are used interchangeably. The relationship between baud rate and bit rate depends on the sophistication of the modulation scheme used to manipulate the carrier. The bit rate (bits per second or bps) and baud rate can be the same, if each bit is represented by a signal transition in a single-bit modulation scheme. Baud rate is almost always a lower figure than bps for a given digital signal because some signal modulation techniques allow more than one data bit to be transmitted per change state. So the bit rate (bps) and baud rate (baud per second) can be connected by the formula: …………………… (1)
The number of bit per baud is determined by the modulation technique. The following two examples give how it could be. 1) When FSK ("Frequency Shift Keying", a transmission technique) is used, each baud transmits one bit; only one change in state is required to send a bit. Thus, the modem's bps rate is equal to the baud rate. 26
2) When we use a baud rate of 2400, you use a modulation technique called phase modulation that transmits four bits per baud. So,
Such modems are capable of 9600 bps operation. Common baud rates for telephone lines are 14400, 28800, and 33600. Baud rates greater than these are possible, but these rates reduce the distance by which devices can be separated.
Figure 6: An Illustration of Baud Rate
3.6.2 Data bits
When the computer sends a packet of information, the amount of actual data may not be a full 8 bit. Standard values for the data packets are 5, 7, and 8 bits. Which setting that is configured depends on what information you are transferring. For example, standard ASCII has values from 0 to 127 (7 bits). Extended ASCII uses 0 to 255 (8 bits). If the data being transferred is a simple text (standard ASCII), then sending 7 bits of data per packet is sufficient for communication, otherwise 8 bits of data per packet is utilised. A packet refers to a single byte transfer, including start or stop bits, data bits, and parity. Since the number of actual bits depends on the protocol selected, the term packet is used to cover all instances. 3.6.3 Start and Stop (Synchronisation) bits:
Stop bit is used to indicate the end of a single packet. Typical values are 1, 1.5, and 2 bits. Since the data is clocked across the lines and each device has its own clock, it is possible for the two devices to become slightly out of sync. Therefore, the stop bits 27
not only indicate the end of transmission but also give the computers some room for error in the clock speeds. The more bits that are used for stop bits, the greater the lenience in synchronizing the different clocks, but the slower the data transmission rate. Start bit is the bit, which signals the receiver that data is coming. Every byte of data in an asynchronous serial transmission is preceded by a start bit and followed by a stop bit.
Figure 7: A Frame with the start and stop shown
3.6.4 Parity
It's used for error checking in serial communication. There are two types of parity: even and odd. And the option of using no parity is also available. For even and odd parity, the serial port will set the parity bit (the last bit after the data bits) to a value to ensure that the transmission has an even or odd number of logic high bits. For example, let us take the data as 011.Then for even parity; the parity bit would be 0 to keep the number of logic high bits even. Similarly, for odd parity the parity bit would be 1, resulting in three logic high bits.
Figure 8: Parity Bits
28
3.7
Examples of Serial Communication Standards
3.7.1 RS-232
Originally, RS-232 is a standard for serial communication transmission of data. It formally defines the signals connecting between a DTE (data terminal equipment) such as a computer terminal, and a DCE (data circuit-terminating equipment, originally defined as data communication equipment
[8]
), such as a modem as it was
originally designed for telecommunication. The RS-232 standard is commonly used in computer serial ports. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pin-out of connectors. However, an RS-232 serial port was once a standard feature of a personal computer, used for connections to modems, printers, mice, data storage, uninterruptible power supplies, and other peripheral devices. However, RS-232 is hampered by low transmission speed, large voltage swing, and large standard connectors. In modern personal computers, USB has displaced RS-232 from most of its peripheral interface roles. Many computers do not come equipped with RS-232 ports and must use either an external USB-to-RS-232 converter or an internal expansion card with one or more serial ports to connect to RS-232 peripherals. Nevertheless, RS-232 devices are still used, especially in industrial machines, networking equipment and scientific instruments
[9]
.
Figure 9: RS-232 port with a DB-25 connector (female)
29
3.7.2 RS-422 RS-422, also known as TIA/EIA-422, is a technical standard originated by the Electronic Industries Alliance that specifies electrical characteristics of a digital signaling circuit. Differential signaling can transmit data at rates as high as 10 Mbit/s, or may be sent on cables as long as 1500 meters. Some systems directly interconnect using RS-422 signals, or RS-422 converters may be used to extend the range of RS-232 connections. The standard only defines signal levels; other properties of a serial interface, such as electrical connectors and pin wiring, are set by other standards.
[10]
A common use of RS-422 is for RS-232 extenders. An RS-232-compatible variant of RS-422 using a mini-DIN-8 connector was widely used on Macintosh hardware until it (and ADB) was replaced by Universal Serial Bus on the iMac in 1998. Broadcast automation systems and post-production linear editing facilities use RS422A to remotely control the players/recorders located in the central apparatus room. In most cases the Sony 9-pin connection is used, which makes use of a standard DE9 connector. This is a de facto industry standard connector for RS-422 used by many manufacturers.
Figure 10: RS-422 with a DB-9 Connector
30
3.7.3 RS-423 RS/EIA/TIA-423 is a standard for serial communications. It defines an unbalanced (single-ended) interface (similar to RS-232), with a single, unidirectional sending driver, and allows for up to 10 receivers (similar to RS-422). It is normally implemented in integrated circuit technology and can also be employed for the interchange of serial binary signals between DTE & DCE. There is no common pinout for RS-423. The BBC (British Broadcasting Cooperation) Micro-computer used a 5-pin DIN connector. DEC (Disaster Emergency Committee) used it extensively with a Modified Modular Jack connector. This was sometimes called "DEC-423".
[11]
Figure 11: An RS-423 cable with a DB-9 and a DB-25 pin out
3.7.4 RS-485 TIA-485-A, also known as ANSI/TIA/EIA-485, TIA/EIA-485, EIA-485 or RS-485, is a standard defining the electrical characteristics of drivers and receivers for use in balanced
digital
multipoint
systems.
The
standard
is
published
by
the
Telecommunications Industry Association/Electronic Industries Alliance (TIA/EIA). Digital communications networks implementing the EIA-485 standard can be used effectively over long distances and in electrically noisy environments. Multiple receivers may be connected to such a network in a linear, multi-drop configuration. These characteristics make such networks useful in industrial environments and similar applications. [12] 31
RS-485 enables the configuration of inexpensive local networks and multi-drop communications links. It offers data transmission speeds of 35 Mbit/s up to 10 m and 100 Kbit/s at 1200 m. Since it uses a differential balanced line over twisted pair (like RS-422), it can span relatively large distances (1,200 m). A rule of thumb is that the speed in bit/s multiplied by the length in meters should not exceed 108. Thus a 50 meter cable should not signal faster than 2 Mbit/s.
[13] [14]
Figure 12: An RS 232 to RS 485 Converter
RS-485 signals are used in a wide range of computer and automation systems. In a computer system, SCSI-2 and SCSI-3 may use this specification to implement the physical layer for data transmission between a controller and a disk drive. RS-485 is used for low-speed data communications in commercial aircraft cabins vehicle bus. It requires minimal wiring, and can share the wiring among several seats, reducing weight. RS-485 is used as the physical layer underlying many standard and proprietary automation protocols used to implement Industrial Control Systems, including the most common versions of Modbus and Profibus. These are used in programmable logic controllers and on factory floors. Since it is differential, it resists electromagnetic interference from motors and welding equipment. In theatre and performance venues RS-485 networks are used to control lighting and other systems using the DMX512 protocol. 32
RS-485 is also used in building automation as the simple bus wiring and long cable length is ideal for joining remote devices. It may be used to control video surveillance systems or to interconnect security control panels and devices such as access control card readers. It can also be used in model railway: controlling the layout in a network/PC environment, connectors in this case are 8P8C / RJ45. Although many applications use RS-485 signal levels; the speed, format, and protocol of the data transmission is not specified by RS-485. Interoperability of even similar devices from different manufacturers is not assured by compliance with the signal levels alone. RS-485 does not specify any connector or pin-out. Circuits may be terminated on screw terminals, D-subminiature connectors, or other types of connectors. However, there is a common pin labeling that applies to all connectors which is; A (inverting pin), B (non-inverting pin), SC (reference pin). The SC line is the optional voltage reference connection. This is the reference potential used by the transceiver to measure the A and B voltages. The B line is positive (compared to A) when the line is idle (i.e., data is 1).
[15]
3.7.5 USB (Universal Serial Bus) Universal Serial Bus (USB) is an industry standard developed in the mid-1990s that defines the cables, connectors and communications protocols used in a bus for connection, communication, and power supply between computers and electronic devices.
[16]
USB was designed to standardize the connection of computer peripherals (including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters) to personal computers, both to communicate and to supply electric power. It has become commonplace on other devices, such as 33
smartphones, PDAs and video game consoles.[17] USB has effectively replaced a variety of earlier interfaces, such as serial and parallel ports, as well as separate power chargers for portable devices. The designers of this standard are Compaq, DEC, IBM, Intel, Microsoft, NEC and Nortel. The design of this standard was in 1996 (19 years ago). The production of this standard has been from 1997 to present. Previous standards that superseded the USB are the serial port, parallel port, game port, Apple Desktop Bus, and PS/2 connector. The length of the cable is between 2 – 5 meters (by category), The connectors conventionally have the design specifications of width of 12 mm (Aplug), 8.45 mm (B-plug); 7 mm (mini/micro-USB) and height 4.5 mm (A-plug), 7.78 mm (B-plug, pre-v3.0); 1.5 – 3 mm (mini/micro-USB). Electrical characteristics includes a signal voltage level of 5 V ± 0.25 V and a maximum current output of 0.5 – 0.9 Amps, but for charging devices up to 5 A. Also, the USB is specially designed for data transfer and some of the specifications that facilitate that capability are the packet data transfer ability, it also has a bit rate capacity of 1.5/12/450/5,000/10,000 [18]
Mbit/s depending on the version.
Figure13: A diagram of a USB showing its pinouts
Pin 1 is for the power supply or Vcc, pin 2 is for negative data (-) pin 3 is for positive data (+) pin 4 is the ground pin.
34
3.7.6 Fire Wire (IEEE 1394)
IEEE 1394 is an interface standard for a serial bus for high-speed communications and isochronous real-time data transfer. It was developed in the late 1980s and early 1990s by Apple, who called it FireWire. The 1394 interface is comparable to USB though USB has more market share.
[19]
Apple first included FireWire in some of its
1999 Macintosh models, and most Apple Macintosh computers manufactured in the years 2000 - 2011 included FireWire ports. However, in 2011 Apple began replacing Firewire with the Thunderbolt interface and as of 2014, FireWire has been replaced by Thunderbolt on new Macs.
[20]
The 1394 interface is also known by the brand
i.LINK (Sony), and Lynx (Texas Instruments). IEEE 1394 replaced parallel SCSI in many applications, because of lower implementation costs and a simplified, more adaptable cabling system. The 1394 standard also defines a backplane interface, though this is not as widely used. Common applications of FireWire include military and aerospace vehicles for data bus network in those vehicles. It can also be used for networking but only for ad-hoc terminals (no routers involved except a hub is to be used). The reason that makes FireWire useful in IIDC
Figure 14: A FireWire Cable
(Instrumentation & Industrial Digital Camera) is the FireWire data format standard for live video, and is used by Apple's iSight A/V camera. The system was designed for machine vision systems [check it] but is also used for other computer vision applications and for some webcams. It is also used in iPod and iPhone synchronisation and charging.
[21][22]
3.7.7 Ethernet
Ethernet is a family of computer networking technologies for local area networks (LANs) and metropolitan area networks (MANs). It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3, 35
[23]
and has since been refined to
support higher bit rates and longer link distances. Over time, Ethernet has largely replaced competing wired LAN technologies such as token ring, FDDI, and ARCNET. The primary alternative for contemporary LANs is not a wired standard, but instead a wireless LAN standardized as IEEE 802.11 and also known as Wi-Fi. The major application of Ethernet protocol is the networking capabilities it possesses. Unlike FireWire this is one uses hubs, repeaters, switches and routers. It also has a good capacity of 10 Mbit/s to 1Gbit/s.
Figure 15: A typical Ethernet cable
3.7.8 MIDI
MIDI - Musical Instrument Digital Interface is a technical standard that describes a protocol, digital interface and connectors and allows a wide variety of electronic musical instruments, computers and other related devices to connect and communicate with one another. A single MIDI link can carry up to sixteen channels of information, each of which can be routed to a separate device. MIDI carries event messages that specify notation, pitch and velocity, control signals for parameters such as volume, vibrato, audio panning, cues, and clock signals that set and synchronize tempo between multiple devices. These messages are sent to other devices where they control sound generation and other features. This data can also be recorded into a hardware or software device called a sequencer, which can be used to edit the data and to play it back at a later time.
36
[24]
MIDI technology was standardized in 1983 by a panel of music industry representatives, and is maintained by the MIDI Manufacturers Association (MMA). All official MIDI standards are jointly developed and published by the MMA in Los Angeles, California, US, and for Japan, the MIDI Committee of the Association of Musical Electronics Industry (AMEI) in Tokyo. Common applications of include firstly Instrument control; MIDI was invented so that musical instruments could communicate with each other and so that one instrument can control another. Secondly, it can be used for composition of musical notes
[25]
.
Figure 16: The image of a MIDI port and cable respectively starting from left
3.7.9 IIC or I2C- Inter-Integrated Circuit
The I²C bus was developed in 1982; its original purpose was to provide an easy way to connect a CPU to peripherals chips in a TV set. Peripheral devices in embedded
37
Systems are often connected to the microcontroller as memory-mapped I/O devices. One common way to do this is connecting the peripherals to the microcontroller parallel address and data busses. This results in lots of wiring on the PCB (printed circuit board) and additional ‘glue logic to decode the address bus on which all the Figure 17: schematic diagram of the IIC peripherals are connected. In A order to spare microcontroller pins, additional logic and
make the PCBs simpler – in order words, to lower the costs – Philips labs in Eindhoven (The Netherlands) invented the ‘Inter -Integrated Circuit, IIC or I²C protocol that only requires two wires for connecting all the peripheral to a microcontroller. The original specification defined a bus speed of 100 kbps (kilobits per second). The specification was reviewed several times, notably introducing the 400 kbps speed in 1995 and – since 1998, 3.4 Mbps for even faster peripherals.
[26]
3.7.10 SPI-Serial Peripheral Interface
The Serial Peripheral Interface (SPI) bus is a synchronous serial communication interface specification used for short distance communication, primarily in embedded systems. The interface was developed by Motorola and has become a de facto standard. Typical applications include sensors, Secure Digital cards, and liquid crystal displays. SPI devices communicate in full duplex mode using master-slave architecture with a single master. The master device originates the frame for reading and writing. Multiple slave devices are supported through selection with individual slave select (SS) lines. Sometimes SPI is called a four-wire serial bus, contrasting with three-, two-, and one-wire serial buses. The SPI may be accurately described as a synchronous serial interface,
[27]
but it is different from the Synchronous Serial Interface (SSI) protocol,
38
which is also a four-wire synchronous serial communication protocol, but employs differential signaling and provides only a single simplex communication channel.
Figure 18: A Block diagram of the SPI
3.7.11 PCI Express
Peripheral Component Interconnect Express, officially abbreviated as PCIe, is a high-speed serial computer expansion bus standard designed to replace the older PCI, PCI-X, and AGP bus standards. PCIe has numerous improvements over the older standards, including higher maximum system bus throughput, lower I/O pin count and smaller physical footprint, better performance scaling for bus devices, a more detailed error detection and reporting mechanism (Advanced Error Reporting, [28]
AER
), and native hot-plug functionality. More recent revisions of the PCIe
standard provide hardware support for I/O virtualization. The PCI Express electrical interface is also used in a variety of other standards, most notably in ExpressCard as a laptop expansion card interface, and in SATA Express as a computer storage interface. Format specifications are maintained and developed by the PCI-SIG (PCI Special Interest Group), a group of more than 900 companies that also maintains the conventional PCI specifications. PCIe 3.0 is the latest standard for expansion cards that is in production and available on mainstream personal computers.
39
[28][29]
Figure 19: Image of a board utilizing PCI Express
40
SECTION FOUR 4.1 THE PROCEDURE FOR SERIAL ARDUINO IN CREATING SYSTEMS
COMMUNICATION
IN
The Arduino Uno has a number of facilities for communicating with a computer, another Arduino, or other microcontrollers. The ATmega328 provides UART (universal asynchronous receiver / transmitter) TTL (Transistor-to-Transistor Logic) 5 V serial communication, which is available on digital pins 0 (RX) and 1 (TX). An ATmega8U2 on the board channels this serial communication over USB and appears as a virtual com port to software on the computer. The '8U2 firmware uses the standard USB COM drivers, and no external driver is needed. Arduino has two additional standards of serial communication which includes I2C and the SPI. These two standards are made available for the Arduino to be able to communicate with other Arduinos and ICs as the user may want to use them.
Figure 20: A Block Diagram of the USB to UART Conversion
41
4.2
UART
A UART, universal asynchronous receiver / transmitter is responsible for performing the main task in serial communications with computers. The UART performs serial-to-parallel conversions on data received from a peripheral device and parallel-to-serial conversion on data received from the CPU. The CPU can read the UART status at any time. The UART includes control capability and a processor interrupt system that can be tailored to minimize software management of the communications link. The combination of the name UART TTL is actually the combination of the type serial communication used and the voltage level that is being implemented for communication.
Figure 21: A Block Diagram of the UART standard.
4.3 Applications of Serial Communication in Arduino Serial communication in Arduino has a vast number of applications which includes 1. Modem Applications, 2. Data Transfer between sensors and other ICs, 3. Interfacing with modules, other Arduinos, sensors and PCs, 4. Processing with PCs, 42
5. Debugging the program written on the micro-controller,
4.4
Examples of the utilisation of serial communication in Arduino
4.4.1 Sending Debug Information from Arduino to Computer In the case where a user chooses to send text and data, so that it will be displayed
on a PC so that whatever goes in and out of the Arduino, could be monitored. This can be made possible by using the Arduino IDE, to type the appropriate codes that will activate that functionality.
Figure 22: A real-time Arduino to PC communication
4.4.2 Sending Formatted Text and Numeric Data from Arduino
In a situation where a user has the intention of sending a normal text, such task is not difficult when compared to sending a formatted text and numeric data. Arduino uses various data types and therefore can be able to know the data the user expects it to print out. In this scenario it is possible to say here that serial communication can be used to send a vast amount of data irrespective of the type of data it sends. As usual a code is sent to the Arduino for the function to be activated.
43
4.4.3 Receiving serial Data in Arduino
If a user needs to know how the Arduino react to commands or data sent from a computer for the sake of debugging the circuit, this can also be achieved with the help of serial communication. In achieving this it is pertinent to know that it is easy to receive 8-bit values (chars and bytes), because the functions used in the programming uses 8-bit values. The process that actually makes this possible is the conversion of ASCII characters to numerical values and vice-versa. There is a code that activates this ability. [30]
4.4.4 Arduino to Arduino communication
It is possible to chain Arduinos together in such a way as to get communication between the two. Having Arduino-Arduino communication can be useful for many projects, such as having one Arduino to run motors and having another sense the surroundings and then relay commands to the other Arduino. This can be done in several methods, using I2C and Serial Peripheral Interface, to list a few.
Figure 23: Chains of Arduinos connected together through serial communication
44
SECTION FIVE: CONCLUSION Finally, this paper has been able to give attention to a process that has facilitated the development of electronic circuits through the discussion on Serial Communication, by doing so the subject on Serial Communication has not been neglected and should remain a constant field of research in order to create a better standard that will improve its current status. Could there still be a lot more that can be discovered about serial communication in the field of computing? How can this actually improve the applications of embedded electronics? How can this underlying process improve the way many devices communicate in order to achieve complex systems and still be efficient? These are questions that Computer Engineers are to keep asking themselves, so that we can continue to maximize the process of serial communication. This paper has been able to act as an eye opener to this hidden but vital process and calls for more hands to be on deck as researchers and developers improve on serial communication. “Shoot for the moon. Even if you miss, you’ll land among the stars.”- Norman Vincent Peale. There is need to aim to reach the best in the area of Serial Communication, even if it is not reached, something close to it can be achieved and the benefits will be enjoyed by all.
45
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