Serial Communication Introduction max. Embedded. Serial Communication Introduction. Hey folks Guess whatWindows Serial Communications component library for CC. C developer tool for serial port communications programs Supports RS232, multidrop RS422 and RS485 ports. Replies to How to enable FTDI Support for your USB Host featuring Honeycomb Tablet including sample native application. Its now time for one of the most desired tutorials on max. Embedded the Serial Communication seriesIn these series, we will discuss the basic concepts of serial communication the loopback test, the USARTUART of AVR and then we will proceed towards implementing the SPI and I2. C in AVR. This post will cover the basics of serial communication and will be mostly a theoretical topic. We will do some practical stuff from next tutorial onwards. Lets have a glance at the contents. Contents. What is Communication Before we move on to serial communication, lets discuss a bit about communication in general. In simple terms, communication is an exchange of ideas between two individuals. Ideas can be anything and in any form they could be writtenspoken words, in form of media like audiovideo, or if you like sci fi, then it can also in form of telepathy But what does communication between two microcontrollers mean Its simple An exchange of data bitsThere are many protocols for communication which would be discussed later but all of them are based on either serial communication or parallel communication. Why do we need Communication Lets take an example. As kids, we all must have played with those remote controlled toy cars and airplanes. It was pretty fun and fascinating at that time. I am sure that most of us at that time didnt try to figure out how it was possible How could the remote control device in your hand control the car or the aeroplaneWell, of course, the device in your hand sends some data, which is received by the caraeroplane. There is a microcontroller onboard the toy, which interprets the signals and acts accordingly. Correct So far so good, but now it doesnt end here. As grown ups, there are a few more questions which should arise Like how does the device send the signalFrom where is the signal being sent What is actually being sentWho receives it How is it processed Lets take another example. This ones a more common example. You have a file in your mobile and you would like to share it with your friend who is sitting next to youHow would you do it Bluetooth, IR, NFC, LAN or email Mostly people would use Bluetooth. IR is obsolete, NFC is still in developmental phase and isnt available in most devices, LAN needs a Wi. FiLAN network whereas email requires an active Internet connection. The same questions can be put forth here as well how is it send, from where is it sent and to where, what is being sent and how is it processedWell, this is why communication is required And to answer all those questions, several communication protocols have been developed Now lets discuss a little about serial and parallel communication. Serial Communication. Serial Transfer. In Telecommunication and Computer Science, serial communication is the process of sendingreceiving data in one bit at a time. It is like you are firing bullets from a machine gun to a target thats one bullet at a time Parallel Communication. Parallel Transfer. Parallel communication is the process of sendingreceiving multiple data bits at a time through parallel channels. It is like you are firing using a shotgun to a target where multiple bullets are fired from the same gun at a time Serial vs Parallel Communication. Now lets have a quick look at the differences between the two types of communications. Serial Communication. Parallel Communication. One data bit is transceived at a time. Multiple data bits are transceived at a time. Slower. 2. Faster. Less number of cables required to transmit data. Higher number of cables required. Serial vs Parallel. So these were the basic differences between serial and parallel communication. From the above differences, one would obviously think that parallel communication is far better than serial communication. But wait, these are just the basic differences. Before we proceed further, we need to be acquainted with a few terminologies Bit Rate It is the number of bits that are transmitted sentreceived per unit time. Clock Skew In a parallel circuit, clock skew is the time difference in the arrival of two sequentially adjacent registers. To explain it further, let us take the machine gun example again. When, say around 5 people are firing at the same time, there is bound to be a time difference in the arrival of the bullet from the first shooter and that from the second shooter and so on. This time difference is what we call clock skew. This is better illustrated in the picture below There is a time lag in the data bits through different channels of the same bus. Clock skew is inevitable due to differences in physical conditions of the channels, like temperature, resistance, path length, etc. Crosstalk Phenomenon by which a signal transmitted on one channel of a transmission bus creates an undesired effect in another channel. Undesired capacitive, inductive, or conductive coupling is usually what is called crosstalk, from one circuit, part of a circuit, or channel, to another. It can be seen from the following diagram that clock skew and crosstalk are inevitable. Major Factors Limiting Parallel Communication. Before the development of high speed serial technologies, the choice of parallel links over serial links was driven by these factors Speed Superficially, the speed of a parallel link is equal to bit ratenumber of channels. In practice, clock skew reduces the speed of every link to the slowest of all of the links. Cable length Crosstalk creates interference between the parallel lines, and the effect only magnifies with the length of the communication link. This limits the length of the communication cable that can be used. These two are the major factors, which limit the use of parallel communication. Advantages of Serial over Parallel. Although a serial link may seem inferior to a parallel one, since it can transmit less data per clock cycle, it is often the case that serial links can be clocked considerably faster than parallel links in order to achieve a higher data rate. A number of factors allow serial to be clocked at a higher rate Clock skew between different channels is not an issue for un clocked asynchronous serial communication links. A serial connection requires fewer interconnecting cables e. The extra space allows for better isolation of the channel from its surroundings. Crosstalk is not a much significant issue, because there are fewer conductors in proximity. In many cases, serial is a better option because it is cheaper to implement. Many ICs have serial interfaces, as opposed to parallel ones, so that they have fewer pins and are therefore less expensive. It is because of these factors, serial communication is preferred over parallel communication. How is Data sent Serially Since we already know what are registers and data bits, we would now be talking in these terms only. If not, I would recommend you to first take a detour and go through the introduction of this post by Mayank. When a particular data set is in the microcontroller, it is in parallel form, and any bit can be accessed irrespective of its bit number. When this data set is transferred into the output buffer to be transmitted, it is still in parallel form. This output buffer converts this data into Serial data PISO Parallel In Serial Out, MSB Most Significant Bit first or LSB Least Significant Bit first as according to the protocol. New. Soft. Serial  Arduiniana. A New Software Serial Library for Arduino. News New. Soft. Serial is in the core Starting with Arduino 1. December, 2. 01. 1, New. Soft. Serial has replaced the old Software. Serial library as the officially supported software serial library. This means that if you have 1. To port your code to 1. New. Soft. Serial references to Software. Serial. New. Soft. Serial is the latest of three Arduino libraries providing soft serial port support. Its the direct descendant of ladyadas AFSoft. Serial, which introduced interrupt driven receives a dramatic improvement over the polling required by the native Software. Serial. Without interrupts, your programs design is considerably restricted, as it must continually poll the serial port at very short, regular intervals. This makes it nearly impossible, for example, to use Software. Serial to receive GPS data and parse it into a usable form. Your program is too busy trying to keep up with NMEA characters as they arrive to actually spend time assembling them into something meaningful. This is where AFSoft. Serials and New. Soft. Darkness 2 Iso more. Serials interrupt architecture is a godsend. Using interrupt driven RX, your program fills its buffer behind the scenes while processing previously received data. Open Source Faq Generator Software here. Improvements. New. Soft. Serial offers a number of improvements over Software. Serial It inherits from built in class Print, eliminating some 4 6. It implements circular buffering scheme to make RX processing more efficient. It extends support to all Arduino pins 0 1. Arduino Mini, not just 0 1. It supports multiple simultaneous soft serial devices. It provides a boolean overflow method to detect buffer overflow. Higher baud rates have been tuned for better accuracy. It supports the ATMega. It supports 8. MHz processors. It uses direct port IO for faster and more precise operation. New with version 1. It supports software signal inversion. New It supports 2. MHz processors. New It runs on the Teensy and Teensy. New It supports an end method as a complement to begin. Be circumspect about using 3. The interrupt handler at these rate becomes so lengthy that timer tick interrupts can be starved, causing millis to stop working during receives. Using Multiple Instances. There has been considerable support for an library that would allow multiple soft serial devices. However, handling asynchronously received data from two, three, or four or more serial devices turns out to be an extremely difficult, if not intractable problem. Imagine four serial devices connected to an Arduino, each transmitting at 3. As bits arrive, Arduinos poor little processor must sample and process each of 4 incoming bits within 2. Yikes It occurred to me, though, that multiple instances could still be possible if the library user were willing to make a small concession. New. Soft. Serial is written on the principle that you can have as many devices connected as resource constraints allow, as long as you only use one of them at a time. If you can organize your program code around this constraint, then New. Soft. Serial may work for you. What does this mean, exactlyWell, you have to use your serial devices serially, like this include lt New. Soft. Serial. h. Heres a GPS device connect to pins 3 and 4. New. Soft. Serial gps4,3. A serial thermometer connected to 5 and 6. New. Soft. Serial therm6,5. An LCD connected to 7 and 8. New. Soft. Serial LCD8,7 serial LCD. GPS unit for a few seconds. LCD becomes the active device here. LCD. listen. LCD. Data gathered. In this example, we assume that readgpsdata uses the gps object and readthermometerdata uses the therm object. Any time you call the listen method, it becomes the active object, and the previously active object is deactivated and its RX buffer discarded. An important point here is that object. This means that you cant write code like this void loop. This code will never do anything but activate one device after the other. Signal InversionNormal TTL serial signaling defines a start bit as a transition from high to low logic. Logical 1 is high, 0 is low. But some serial devices turn this logic upside down, using what we call inverted signaling. As of version 1. New. Soft. Serial supports these devices natively with a third parameter in the constructor. New. Soft. Serial my. Inverted. Conn7, 5, true this device uses inverted signaling. New. Soft. Serial my. GPS3, 2 this one doesnt. Library Version. You can retrieve the version of the New. Soft. Serial library by calling the static member libraryversion. New. Soft. Serial libraryversion Resource Consumption. Linking the New. Soft. Serial library to your application adds approximately 2. Download. The latest version of New. Soft. Serial is available here New. Soft. Serial. 12. Note dont download this if you have Arduino 1. As of 1. 0, New. Soft. Serial is included in the Arduino core named Software. Serial. Change Loginitial versionported to Arduino 0. RX buffer overflow has occurred, and c tuned RX and TX for greater accuracy at high baud rates 3. K, 5. 7. 6. K, and 1. K. minor bug fixes add. OSX avr gcc 4. 3. MHz support and flush and enabletimer. IO.   Revised routines now get perfect RX up to 5. K on 1. 6MHz processors and 3. K on 8. MHz processors. TTL signalling supported. MHz processors supported. Teensy and Teensy supported. New end method and destructor added to clean up. Acknowledgements. Many thanks to David Mellis, who wrote the original Software. Serial, and to the multi talented ladyada, whose work with AFSoft. Serial is seminal. Ladyada also provided the Goodnight, moon example sketch, fixed a problem with the interrupt naming see v. NSS with the 3. 28p. Thanks also to rogermm and several other forum users who have tested New. Soft. Serial and given useful feedback. The diligent analysis of forum user etracer yielded the root cause of a tricky problem with NSS on OSX. A bug in avr gcc 4. NSS 5. User jin contributed a large body of work based on NSS and identified a potential problem that could result in data loss fixed in NSS 5. NSS that supports 4 pin serial, with the additional pins providing a very nice RTSCTS flow control. We may see this in NSS in the near future. Thanks to Garret Mace, who contributed the delay tables for 2. MHz processors and claims that he can send and receive at 1. K baud.   Cool Thanks to Paul Stoffregen, both for his fine work with Teensy and Teensy, and for contributing some useful suggestions that help New. Soft. Serial run on them without modification. I appreciate any and all input.