IV B.Tech. I Sem (R15) ECE : Embedded Systems : UNIT -3



UNIT – 33.1. Embedded hardware and various building blocks3.2. Processor Selection for an Embedded System3.3. Interfacing Processor, Memories and I/O Devices3.4. I/O devices and I/O interfacing concepts3.5. Serial Bus Communication protocols 3.6. I/O Buses b/w networked multiple devices3.7. Timer and Counting Devices 3.8. Embedded System development process and design cycle3.9. Use of Software Tools and IDE for Development of an Embedded System 3.10. Emulator and In-Circuit Emulator (ICE)3.11. Issues in Hardware- Software Design and Co-design 3.12. Design metrics of embedded systems - low power, high performance, cost, time-to-market.2.1. . Embedded hardware and various building blocks:3.5. Communication Interface / Serial bus communication Protocols Communication interface is required to interface an embedded system with external world. The need for communication interfaces are to communicate with host system/PC/work stationto send/receive data to other embedded systemto interact with another system for sharing datato share data with other embedded systems which are connected to a networkto connect to internet so that anyone can access the embedded systemThe different types of communication interfaces are given below. These interfaces provide different functionality and different data transmission rates.I2C busSPI busCAN busUARTUSB1-wire interfaceEthernetInfraredBluetoothZigBeeA?Controller Area Network?(CAN bus) is a robust?vehicle bus?standard designed to allow?microcontrollers?and devices to communicate with each other in applications without a?host computer. It is a?message-based protocol, designed originally for?multiplex?electrical wiring within automobiles to save on copper, but is also used in many other contexts.CAN is a?multi-master?serial bus?standard for connecting Electronic Control Units [ECUs] also known as nodes. Two or more nodes are required on the CAN network to communicate. The complexity of the node can range from a simple I/O device up to an embedded computer with a CAN interface and sophisticated software. The node may also be a gateway allowing a standard computer to communicate over a USB or Ethernet port to the devices on a CAN network.Each node requires a:Central processing unit, microprocessor, or host processorThe host processor decides what the received messages mean and what messages it wants to transmit.Sensors, actuators and control devices can be connected to the host processor.CAN controller; often an integral part of the microcontrollerReceiving: the CAN controller stores the received serial bits from the bus until an entire message is available, which can then be fetched by the host processor (usually by the CAN controller triggering an interrupt).Sending: the host processor sends the transmit message(s) to a CAN controller, which transmits the bits serially onto the bus when the bus is free.Transceiver?Defined by ISO 11898-2/3 Medium Access Unit [MAU] standardsReceiving: it converts the data stream from CANbus levels to levels that the CAN controller uses. It usually has protective circuitry to protect the CAN controller.Transmitting: it converts the data stream from the CAN controller to CANbus levels.Each node is able to send and receive messages, but not simultaneously. A message or?Frame?consists primarily of the ID (identifier), which represents the priority of the message, and up to eight data bytes. A CRC, acknowledge slot [ACK] and other overhead are also part of the message. The improved CAN FD extends the length of the data section to up to 64 bytes per frame. The message is transmitted serially onto the bus using a?non-return-to-zero?(NRZ) format and may be received by all nodes.The devices that are connected by a CAN network are typically?sensors,?actuators, and other control devices. These devices are connected to the bus through a?host processor, a CAN controller, and a CAN transceiver. : Universal Serial Bus Universal Serial Bus (USB) is a high speed serial bus for data communication between host system and peripherals.The Universal Serial Bus was developed to simplify and improve the interface between personal computers and peripheral devices. Because of its wide variety of uses, including support for electrical power, the USB has replaced a wide range of interfaces like the parallel and serial port.FeaturesTrue Plug-and-Play Self configuringHot swapping - plug and unplug without rebootingEasy of useUp to max. 127 physical devicesLow cost cables and connectorsUsesIt connects peripheral devices such as digital camera, mice, keyboard, printer, scanner, media device, modems, joysticks, external hard drive and flash memory cards etc.BandwidthUSB 1.1 : Low Speed - 1.5 Mbit per second - that is mostly used for Human Input Devices such as keyboards, mice, joysticks and often the buttons on higher speed devices such as printers or scanners; - 3mFull Speed - 12 Mbit per second which is widely supported by USB hubsUSB 2.0: Hi-Speed - 480 Mbit per second – 25mUSB 3.0 : Super Speed - 4800 Mbit per second Wireless USB with Ultra Wide Band Technology -480 Mbit per second – 3mThe standard was made to improve?plug and play?devices. This means that a device can be plugged into a free socket, and simply work. The computer will notice the device. The computer sometimes installs special?software?to use the device. The device can be removed after it stops being used. This technology is called "hot swapping". "Hot swapping" means it can be plugged and unplugged while the power is on. The computer does not need to be turned off for people to change the devices.A USB is intended to enhance plug-and-play and allow hot swapping. Plug-and-play enables the operating system (OS) to spontaneously configure and discover a new peripheral device without having to restart the computer. As well, hot swapping allows removal and replacement of a new peripheral without having to reboot.The USB interface is self-configuring, so the user need not adjust settings on the device and interface for speed or data format, or configure interrupts, input/output addresses, or direct memory access channels.Small devices can be powered directly from the USB interface.USB can provide a small amount of power to the attached device through the USB cord. Devices that only need a little power can get it from the bus, and do not need a separate electric power plug. That allows gadgets like USB battery chargers, lights, and fans.Although there are several types of USB connectors for connecting the USB peripheral and host devices, the majority of USB cables are one of two types, Type A and Type B. Type A connector is used for upstream connection (connection with host). It has a flat rectangle interface that inserts into a hub or USB host which transmits data and supplies power. The USB connectors present in desktop PCs / laptops are examples for Type A USB connectors. Type B USB connector is used for downstream connection (connection with slave device). It is square with slanted exterior corners. The type B connector also transmits data and supplies power. Some type B connectors do not have a data connection and are used only as a power connection.Both Type A and Type B connectors contains 4-pins for communication. The pin details for connectors are listed in the table given below.USB has 4 shielded wires: Two for power (+5v & GND) and Two for differential data signals (labelled as D+ and D- in pin out).In a USB data cable Data+ and Data- signals are transmitted on a twisted pair with no termination needed. Half-duplex differential signalling is used to reduce the effects of electromagnetic noise on longer lines. D+ and D- operate together; they are not separate simplex connections.A USB device must indicate its speed by pulling either the D+ or D- line high to 3.3 volts. These pull up resistors at the device end will also be used by the host or hub to detect the presence of a device connected to its port. Without a pull up resistor, USB assumes there is nothing connected to the bus.The Universal Serial Bus is a network of attachments connected to the host computer. These attachments come in two types known as Functions and Hubs.?Functions?are the peripherals such as mice, printers, etc.?Hubs basically act like a double adapter does on a power-point, converting one socket, called a?port, into multiple ports. Hubs and functions are collectively called?devices.?The host has a hub embedded in it called the?root hub, and in practical implementations hubs are usually combined with one or more functions, such as keyboards or monitors. These are called?compound devices?and act like a hub with the functions permanently connected, along with any additional ports. Hubs may be connected to other hubs in a tiered arrangement, but the bus topology still applies.centercenterUSB has a strict "tree" topology and "master-slave" protocol for addressing peripheral devices; peripheral devices cannot interact with one another except via the host, and two hosts cannot communicate over their USB ports directly.A USB system consists of a host with one or more downstream ports, and multiple peripherals, forming a tiered-star topology. Up to 127 devices may be connected to a single host controller.A USB interface can be designed to provide the best available latency for time-critical functions, or can be set up to do background transfers of bulk data with little impact on system resources.Isochronous transfersAt some guaranteed data rate (for fixed-bandwidth streaming data) but with possible data loss (e.g., realtime audio or video)Interrupt transfersDevices that need guaranteed quick responses (bounded latency) such as pointing devices,?mice, and keyboardsBulk transfersLarge sporadic transfers using all remaining available bandwidth, but with no guarantees on bandwidth or latency (e.g., file transfers) ................
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