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Computer Interfacing 1 Interfaces and Interfacing . Definitions of “interface” from Webster’s Dictionary: . noun: the place at which independent systems meet and act or communicate with each other Examples: human - machine interface (analogue-machine interface), terminal - network interface (TTL - CMOS interface), parallel or serial interface . Informal Definition i) The physical, electrical and logical means of exchanging Information with a functional module ii) The process of enabling a computer to communicate with the external world through Software, Hardware and Protocols 2 . An interface is a device and/or set of rules to match the output of one device to send information to the input of another device . physical connection . the hardware . rules and procedures . the software . Interfacing is the process of connecting devices together so that they can exchange information . The process of reading input signals and sending output signals is called I/O . I/O conventions . I/O direction is relative to the MCU . Input is data read by the MCU . Output is data sent out by the MCU 3 Interfaces and Interfacing A microcontroller (sometimes abbreviated µC, uC or MCU) Why is computer interfacing important ? 1. The human - machine interface determines the ultimate success or failure of many computer- based systems 2. Digital systems exist within and must successfully interact with an analogue natural environment (Digital – analogue interfaces are unavoidable) 3. Rather than designing digital systems from elementary components, computer engineers more typically assemble new systems from existing subsystems 4 Typical Interfacing Activities . Selecting software/hardware subsystems that can (at least potentially) interact well with each other . Appropriate D/A and A/D converters (speed, accuracy, .) . Serial vs. parallel communication . Providing appropriate hardware connections . Selecting cabling, connectors, drivers, receivers, correct termination, etc. . Resolving any hardware incompatibilities . CMOS with TTL . Configuring hardware interfaces correctly using low-level software drivers . LCD, Keypads in embedded systems (Liquid Crystal Display-LCD) . Interfacing software components correctly . Selecting compatible software versions . Calling the correct procedures in the correct sequence with the correct parameters 5 6 SERIAL COMMUNICATION Typical Interfacing Activities PARALLEL COMMUNICATION Connectors Transducer and receiver What is Termination? Termination, in its most basic sense, is the connection of a cable to a source or destination device. For low frequency applications, this may involve simply putting the individual wires in a connector and attaching the connector to the device. At higher frequencies, termination can also take a second meaning. To first understand termination you need to understand impedance. In many systems, such as Broadband/CATV or broadcast video, signals are split to go in different directions. Each of the splits (outputs) must "see" the correct impedance. Normally, one would simply attach a cable of the correct impedance to each of the outputs of the device. But it can sometimes happen that there are more splits than desired. In that case, those unused outputs must be "terminated" with the correct impedance. To accomplish this, you attach a connector which contains a resistor inside chosen to mimic the correct impedance. In other words, you fool that output into thinking a cable is attached, when in fact, there is none! If you do not terminate unused outputs, they can radiate, and that signal can cause noise and interference in other nearby equipment. 7 Typical Interfacing Activities For RF applications, or for extremely long signal runs, such as telephone circuits, impedance matching is essential. Matched impedances mean that the source, cable and load impedances are all the same. • CMOS with TTL Complementary metal–oxide–semiconductor (CMOS) is a technology for constructing integrated circuits Transistor–transistor logic (TTL) is a class of digital circuits built from bipolar junction transistors (BJT) and resistors 8 Typical Interfacing Activities • CMOS with TTL 9 Typical Interfacing Activities • CMOS with TTL 10 Typical Interfacing Activities [...]... coax Printed Circuit Board-PCB twisted pair PCB Hardware Interfaces within a Personal Computer (PC) Components of a Computer System Introduction to Microcontroller Embedded System You are used to chips like the Pentium, but in terms of installed machines these are a small portion of total computer use Think how many computers you have at home? Digital cameras, video cameras, TVs, mobile phones, calculators,... Microcontrollers sometimes are called single-chip computers because they have on-chip memory and I/O circuitry and other circuitries that enable them to function as small standalone computers without other supporting circuitry Microcontroller The key features of microcontrollers include: High Integration of Functionality Microcontrollers sometimes are called single-chip computers because they have on-chip memory... and a demonstration board Some packages include a high level language compiler such as a C compiler and more sophisticated libraries Microcontroller, Microprocessor and Microcomputer A microcontrollers are is like a single chip computers that are often embedded into other systems to function as processing/controlling unit Microcontrollers are used in a wide number of electronic systems such as: Engine... communicate with each other Every information transfer is an output from one device and an input into another For instance, on a computer, a keyboard and mouse are considered input devices while monitors and printers are considered output devices Typical devices for communication between computers, such as modems and network cards, operate as both input and output devices I/O can be: A number of digital...Typical Interfacing Activities • CMOS with TTL System-Level Interfaces Human-machine interface Input devices: keyboard, mouse, microphone, camera Output devices: CRT, printer, light panel, audio amp Cathode... of Functionality Microcontrollers sometimes are called single-chip computers because they have on-chip memory and I/O circuitry and other circuitries that enable them to function as small standalone computers without other supporting circuitry Field Programmability, Flexibility Microcontrollers often use EEPROM or EPROM as their storage device to allow field programmability so they are flexible... The PICmicro was originally designed around 1980 by General Instrument as a small, fast, inexpensive embedded microcontroller with strong I/O capabilities Characteristics of Embedded System Embedded computers have to be very low cost, simple and reliable They can not use any moving parts (disk drives) because: 1 power hungry 2 bulky 3 expensive Features of Embedded System Program in Read Only Memory... set of instructions to carry out user defined tasks The ability to be able to access external memory chips to both read and write data from and to the memory Microcontroller, Microprocessor and Microcomputer Types of Memory can be obtained as either: Read Only Memory (ROM) This is memory that can only be read, the data being stored in the memory device during its manufacture Once data has been... times over Electrically Erasable Programmable Read Only Memory (EEPROM) Similar to EPROM but has part or all of the memory contents erased by the microprocessor Microcontroller, Microprocessor and Microcomputer Both ROM and EPROM memory are used to hold the program code of a microprocessor used in an embedded system, ie a microprocessor used in an application where the program code is always the same... read-write memories were sequential, and did not allow random access RAM memory is used to store dynamic data (that will change during the operation of the program) Microcontroller, Microprocessor and Microcomputer RAM takes the form of integrated circuits that allow the stored data to be accessed in ANY order That is, at random and without the physical movement of the storage medium or a physical reading . Computer Interfacing 1 Interfaces and Interfacing . Definitions of “interface” from Webster’s. MCU 3 Interfaces and Interfacing A microcontroller (sometimes abbreviated µC, uC or MCU) Why is computer interfacing important ? 1. The human - machine