Unit 2 Avionics
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Transcript of Unit 2 Avionics
Avionics Unit-2 PRINCIPLES OF DIGITAL SYSTEMSDigital Computers-Digital Number System-Number system and Codes Fundamentals of Logic and Combinational Logic CircuitsDigital Arthmatic- Interfacing with Analog System Microprocessors & Memories
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Syllabus-Unit 21. Digital Computers-Digital Number System-Number system and Codes 2. Fundamentals of Logic and Combinational Logic Circuits-Digital Arthmatic- Interfacing with Analog System 3. Microprocessors & Memories
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Analog & Digital Systems1. Continuous time varying signal 2. Require a medium for transmission 3. More Noisy 4. Subject to attenuation 5. Not a flexible system 1. Discrete digital signal 2. Signal sampled and quantized before transmission 3. Free from Noise 4. Not subjected to attenuation 5. Highly flexible system3
Advantages of digital systems in avionics-20091. Excellent display technology LCD or AMLCD 2. Excellent Flight Instrumentation system in digital as in Airbus & Boeing 3. Compression of data possible in Digital system 4. Synchronizing image with Data 5. Excellent interface with Core Memory 6. Possible to have open system as in ARINC 629, 1553 B
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Difficulties in Digital Data-2008 Nov Digitizing analog data Losses Interface between data and data users Privacy and network environment Security requirements Operational Models & Programs Standardization requirement
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Number SystemsTypes and Conversion from one to the other
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Common Number SystemsSystem Bas e Decimal 10Binary 2
Symbols0, 1, 9 0, 1
Used by Used in humans computers? ? Yes No No Yes
OctalHexadecimal
816
0, 1, 70, 1, 9, A, B, F
NoNo
NoNo
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Conversion Among Bases The possibilities:Decimal Octal
Binary
Hexadecimalpp. 40-468
Quick Example
2510 = 110012 = 318 = 1916Base
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Binary to DecimalDecimal Octal
Binary
Hexadecimal
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Example-Convert 101011 to decimelBit 0 1010112 => 1 1 0 1 0 1 x x x x x x 20 21 22 23 24 25 = = = = = = 1 2 0 8 0 32 4310
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Decimel to Binary12510 = ?2 2 125 2 62 2 31 2 15 7 2 3 2 1 2 0 1 0 1 1 1 1 1
12510 = 11111012
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Octal to Decimal Technique Multiply each bit by 8n, where n is the weight of the bit The weight is the position of the bit, starting from 0 on the right Add the results
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Example-convert 724 to decimel7248 => 4 x 80 = 2 x 81 = 7 x 82 = 4 16 448 46810
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Octal to Decimal Convert 1256 in Octal to Decimel 1 2 5 6= 6 x 80 + 5 x 81 + 2 x 82 + 1 x 83 = 6 + 40 + 128 + 512 = 686
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Hexadecimal to DecimalDecimal Octal
Binary
Hexadecimal
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Hexadecimal to Decimal Technique Multiply each bit by 16n, where n is the weight of the bit The weight is the position of the bit, starting from 0 on the right Add the results
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Example
ABC16 =>
C x 160 = 12 x 1 = 12 B x 161 = 11 x 16 = 176 A x 162 = 10 x 256 = 2560 274810
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Tutorial1. Convert 10111, 10111001 to Binary Ans=23, 185 2. Convert 88 to Binary-ans 01011000 3. Convert Decimel 22, 65 to Hexadecimel Ans= 16,41 4. Convert Hexadecimel 22, 34, 82 to decimel-Ans=34, 52, 130
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CodesBasic types
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Types of Codes1. 2. 3. 4. Binary Coded Decimel- BCD Excess 3 Code Gray Code Alphanumeric Codes- containing Alphabets and Symbols like @, $, % etc in ASCII form American Standard Code for Information Interchange 5. Error Detecting and Correction Codes21
FLOATING POINT NUMBERS (2/4)
3 parts: sign, mantissa and exponent The base (radix) is assumed to be 2. Sign bit: 0 for positive, 1 for negative.sign mantissa exponent
CS2100
Number Systems and Codes
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LOGIC AND COMBINATIONAL LOGIC
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Basic Logic Gates and Basic Digital Design NOT, AND, and OR Gates NAND and NOR Gates DeMorgans Theorem Exclusive-OR (XOR) Gate Multiple-input Gates
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NOT Gate -- InverterNOT X Y = ~X Y
X 0 1
Y 1 0
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AND GateAND X Z Y Z = X & Y X 0 0 1 1 Y 0 1 0 1 Z 0 0 0 1
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AND Operation Boolean expression for the AND operation: x =A B The above expression is read as x equals A AND B
Enable/Disable (inhibit) Circuit
NAND GateNAND X Z Y Z = ~(X & Y) nand(Z,X,Y) X 0 0 1 1 Y 0 1 0 1 Z 1 1 1 0
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OR GateOR X Y Z = X | Y Z X 0 0 1 1 Y 0 1 0 1 Z 0 1 1 1
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OR Operation Boolean expression for the OR operation: x =A + B The above expression is read as x equals A OR B Figure 3-2
Example 3-1 Using an OR gate in an alarm system(refer to Fg03-04.ckt)
NOR GateNOR X Y Z X 0 0 1 1 Y 0 1 0 1 Z 1 0 0 0
Z = ~(X | Y) nor(Z,X,Y)
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De Morgans Theorem-1~(X & Y) = ~X | ~YNOT all variables Change & to | and | to & NOT the result
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DeMorgans TheoremsDeMorgans Theorems are two additional simplification techniques that can be used to simplify Boolean expressions. Again, the simpler the Boolean expression, the simpler the resulting logic.
A B A B A B A B3535
NOR GateXY Z X Z Y
Z = ~(X | Y) X 0 0 1 1 Y 0 1 0 1 Z 1 0 0 0
Z = ~X & ~YX 0 0 1 1 Y ~X ~Y 0 1 1 1 1 0 0 0 1 1 0 0 Z 1 0 0 036
Exclusive-OR Gate
XOR X Z Y Z = X ^ Y xor(Z,X,Y)
X Y0 0 1 1 0 1 0 1
Z0 1 1 0
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Logic Families DTL logic TTL logic RTL logic CMOS logic
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Available ICs
COMBINATIONAL LOGIC Combinational logic circuit receive binary information on a single input and sends this information to one of many possible output lines Single input to Many outputs Output of Combinational Logic depend on Input40
Combinational Circuit-schematic A combinational logic circuit has: A set of m Boolean inputs, A set of n Boolean outputs, and Output depend on current status of Input
A block diagram:Combinatorial Logic Circuit
m Boolean Inputs
n Boolean Outputs41
Demultiplexers . The output is selected by the binary value on the select lines.
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DIGITAL COMPUTERSTypes, and Schematic
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Types of Computer1. Desktop 2. Work Station (Powerful Single User computer) 3. Min Frame Computer-Powerful Multi user computer 4. Super Computer-performing millions of instructions 5. Mini Computer-between Work station and main Frame computer44
Digital Computer
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Schematics of a Digital Computer1. CPU 2. Memory- RAM/ROM 3. Input Port-keyboard, mouse, camera, scanner 4. Output Port-monitor, printer 5. Data Buses- A bus connecting CPU to I/O ports and Memory
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Schematics of a Digital ComputerMemory RAM/ROM Input Port
Output Port
Data Bus
C P U
Control Bus Address Bus
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Elements of a Computer CPU=Mother board, RAM+ ROM Input Port- Keyboard, Mouse, Camera Output Port-Printer Unidirectional Address Bus-carries control information between the CPU and main memory Bi Directional Data Bus-carries data between all the hardware components of the computer Uni directional Control Bus-used by CPUs for communicating with other devices within the computer.48
Parts of a Computer CPU consisting of Mother board- a PCB - the foundation of a computer CPU, RAM to function with each other Mother board has BIOS,CMOS RAM for permanent info. Storage Input/Output devices
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Air Data Computer ADC Determine the calibrated airspeed, Mach number , altitude, and altitude trend data from an aircraft's pitot-static system Computes air data information from the pitot-static pneumatic system, aircraft temperature probe and barometric correction device Designed for FMS, GPS and GPWS applications50
ADC
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Avionics computer/Air Data ComputerFlight Control Appln Landing Gear Appln
Display Control Appln
API
Operating System Board Support Package CPU / IO
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Features of Flight Computer1. Large LCD screen displaying prompts labeled Inputs and outputs 2. Flight planning Menu and execution 3. 16 unit conversions ( mph to NMI etc) 4. Calculating true airspeed, ground speed, mach number, altitudes, fuel, headings and courses, time/speed/distance, winds, headwind/crosswind components, gliding information, and weight and balance 5. Count Down and Count up Timer 6. Clock displaying both local and UTC time53
Features of AMADC ( Modern Digital Aircrafts)-Honeywell On Aircraft Software Loading Can work with Stringent Reduced Vertical Separation Minimum Airspace RVSM Modular Software ARINC 429 input/output Less Effort for Software Upgradation Meeting with DO-178B level testing54
Air Data Computer
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MICROPROCESSORTypes, Architecture and functions
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RISC & CISC Microprocessor CISC-Complex Instruction Set Computerinstruction performing a series of operations inside the processor. CISC-chips easy to program & efficient use of memory.CISC use Macrocodes Eg. IBM 360,(Intel), 8085 family etc RISC Reduced Instruction Set Computer- a type of microprocessor architecture utilizing small, reduced set of instructions-Apple Mackintosh
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Basic Microprocessors1. 2. 3. 4. 5. 8085 8 Bit uP 8086 16 Bit 286 386 & 486 obsolete Pentium I v th generation of 8086 Pentium II to Dual Core Processor
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Specification of Microprocessor1. Risc or Cisc 2. Data Bus speed =8 bit to 256 bit or (x 86) as in Intel and registers (8 bit to 32 Bit) 3. Supply Voltage from -5V to +5V 4. Clock Speed-speed at which devices connected to the Bus operate-3Mhz to 2.5 GHz 5. Number of Input/output ports 6. TCP/IP ports 7. USB ports59
Pentium IV-clock 2.5 GHz
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Pentium Processor
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Manufacturer of Microprocessor Intel-USA-CISC Power PC- RISC-Reduced Instruction Set Computer-32 Bit Motorola 6800-16 Bit & 32 Bit MIP RISC Microprocessor Athelon
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Microprocessor SchemeCP
MPURESET
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Microprocessor Scheme1. Unidirectional Address bus ( 8 bit width , 16 or 32 bit width) sending an address to memory 2. Bidirectional Data bus ( 8, 16 or 32 bits wide) sending data to memory or receive data from memory 3. Unidirectional Control Bus: RD (read) and WR (write) Control bus to get the addressed location 4. Clock for pulse sequence to the processor 5. Reset line resetting the program counter to zero (or whatever) and restarting execution64
Buses in a Desktop
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Microprocessor Scheme1. CPU or central processing unit -- a complete computation engine , fabricated on a single chip. 2. Register- a memory from 8 Bit to 128 Bit 3. ALU- Arithmetic logic unit for all mathematical operations 4. A Clock for set and reset
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Elements of P
1.ALU
2. Register Array
3.Control Unit
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Elements of P1. 2. 3. 4. ALU Register (memory from 8 Bit to 128 Bit Control Unit Buses namely Address Bus, Control Bus & Data Bus 5. A reset line for Resetting and Starting 6. A clock68
Microprocessor Basic
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8085 PBasic features, Architecture,
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8085 General Purpose 8 Bit microprocessor, addressing 64 K Byte memory It is a single chip N Mos Work on +5V at a max frequency of 3 MHZ
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8085 P
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Buses of 80851. 8 Bit Data Bus- Do to D7 going from the CPU to Memory and Input/Output port Bidirectional 2. 16 Bit Address Bus Ao to A15 from CPU to memory and Input/Output Port Unidirectional 3. 16 Bit Control Bus Co to C15
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Architecture of 8085 uP1. 8 Bit Microprocessor 2. 16 Bit Address Bus from Ao to A15 with 216 memory locations=64kBit 3. 8 Line Data Bus from Do to D7 4. 16 Bit Program Counter-PC 5. Has 16 Bit Stack Pointer 6. Require +5V & operating on 3.2 MHz clock74
Architecture of P 8085-8 Bit1) 8 Bit Bi Directional Data Bus for transferring the data to the elements 2) 16 Bit Uni Directional Address Bus for finding a memory location 3) Uni- Directional Control Bus for giving a timing signal to the MPU, I/O devices 4) 8 Bit 6 Registers for Storing the data for program execution 5) 8 Bit Accumulator for Carrying out Arithmatic operations 6) 8 Bit Flag for testing the data75
Architecture of P 8085
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1. Data Bus: Data bus Bi Directional -a group of eight lines D0 to D7 used for data flow. Data flow in both directions between the MPU and memory and peripheral devices. MPU using the data bus to perform the second function: transferring binary information. Eight data lines enable the MPU to manipulate 8-bit data ranging from 00 to FF (28 = 256 numbers). The largest number that can appear on the data bus is 1111 1111.
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Why Data Bus Bi directional microprocessor has to fetch (read) the data from memory or input device for processing and after processing, it has to store (write) the data to memory or output device. Hence the data bus is bi-directional.
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2. Address Bus: Unidirectional address bus a group of 16 lines generally identified as A0 to A15. Address bus bits flow in one directionfrom the MPU to peripheral devices. MPU consisting of ALU,Accumulator and General Purpose Register-using the address bus for identifying a peripheral or a memory location79
Why the Address Bus Unidirectional The address is an identification number used by the microprocessor to identify or access a memory location or I / O device It is an output signal from the processor. Hence the address bus is unidirectional
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3. Control Bus Control bus Unidirectional-carrying synchronization signals and providing timing signals to Memory, Input and Output devices MPU generates specific control signals for every operation performed. Control signals used to identify a device type which the MPU is communicating.81
4. Register 8085 having 6 general-purpose 8 bit registers B,C,D,E,H & L to store 8-bit data for program execution. B,C,D,E,H,L registers combined as register pairs-BC, DE, and HL-for performing some 16-bit operations
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REGISTERS IN 80851. Accumulator register-high order register 2. Temporary register, 3. Instruction register, 4. Stack Pointer-16 bit address register 5. Program Counter83
Register pairs in 8085
1.B-C register pair 2. D-E register pair 3.H-L register pair
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Register, Accumulator and Flag
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Accumulator Accumulator an 8-bit register for arithmetic/logic unit (ALU). Accumulator used to store 8-bit data and to perform arithmetic and logical operations. The result of an operation is stored in the accumulator.
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Purpose of Accumulator in 8085 Accumulator used by 8085 for temporary data storage & manipulation of data and instructions A-an accumulator for execution of a program
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Flag Flag is a flip flop used to store the information about the status of the processor and the status of the instruction executed most recently.
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Status Flags in 8085 1. 2. 3. 4. 5. Flags for testing the data conditions. Sign (S), Zero (Z), Parity (P), Carry (CY), Auxiliary Carry (AC) flags.
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List of Flags in 80851. Sign flag S-sign of a value calculed by arthmatic or logical instructions 2. Zero flag-Z, normally set to 0: and set to 1 if the logical operation is 0 3. Carry flag-CY set when there is carry operation 4. Auxiliary flag AY-set to carry operation similar to CY, but from lower half to uper half 5. Parity flag-P, set to 1 if the parity is even
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1 Byte and 2 Byte Instruction Instructions in Computer in Binary Codes or Machine instruction Instruction of one word size or 8 Bits called 1 Byte Instruction Instruction in two word size of 16 bits is called 2 Byte instruction
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Why Clock required in uP Clock is necessary for synchronizing various internal operations or devices in the microprocessor and to synchronize the microprocessor with other peripherals in the system. 8085 has the clock generation circuit on the chip but an external quartz crystal or L C circuit or RC circuit should be connected at the pins XI and X2. Maximum internal clock frequency of 8085 is 3.03 MHz.92
Difference between 85 and 861. 8 bit data bus 2. Clock speed low 3 MHz 3. 16 Bit address space 4. 64 kBit memory 5. Small No lf Transistors-5000 6. Both operate on 5V 1. 16 bit data bus 2. Clock speed higher 10 MHz 3. 20 Bit Address Space 4. 1 Mb memory 5. Higher no of transistors in memory 30,00093
Interrupts in MicroprocessorTypes and Function
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Interrupt
Interrupt is a signal sent by an external device to the processor so as to request the processor for doing a particular task or work95
Interrupts An emergency asynchronous signal to a Microprocessor where the external device (I/O devices) get the attention of MP when pressing a key on the keyboard or clicking a button on the mouse triggers an interrupt 2 types of Interrupts-Maskable (delayed or rejected) and Non-maskable (cannot be rejected) Also classified as Vectored-Hard wired and Non Vectored-software operated.. 8085 has 5 External Interrupts96
Interrupt Inputs in 8085-5 nos.1. INTR interrupt-Non Vectored 2. RST 5.5,6.5 and 7.5-maskable interrupts 3. TRAP-A non maskable Vectored automatic interrupt
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8085 InterruptsTRAP RST7.5 RST6.5 RST 5.5 INTR
8085
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Software Software interrupts are program instructions. These instructions inserted at desired locations in a program. While running a program, if software interrupt instruction is encountered then the processor executes an interrupt service routine99
Software Interrupts RST0, RST1, RST2, RST3, RST4, RST5, RST6, RST7
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Hardware If an interrupt is initiated in a processor by an appropriate signal at the interrupt pin, then the interrupt is called Hardware interrupt
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Distinction between software and hardware Interrupt Software interrupt is initiated by the main program, but the Hardware interrupt is initiated by an external device. In 8085, the Software interrupt cannot be disabled or masked but the Hardware interrupt except TRAP can be disabled or masked.
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Five Hardware Interrupts in 80851. INTR is maskable 8080A compatible interrupt. 2. RST5.5 is a maskable interrupt for registering into Stack 3. ST6.5 is a maskable interrupt. 4. RST7.5 is a maskable interrupt 5. Trap is a non-mask able highest priority interrupt.103
What is masking and why it is required Masking is preventing the interrupt from disturbing the current program execution. When the processor is performing an important job (process) and if the process should not be interrupted then all the interrupts should be masked or disabled. In processor with multiple 'interrupts, the lower priority interrupt can be masked so as to prevent it from interrupting, the execution of interrupt service routine of higher priority interrupt.104
Purpose of ALE in 8085 ALE-Address Latch Enable Signal
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P used in Avionics MIP7965, 64-bit Super scaler 750MHz MIPS Microprocessor
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MIP 7965 P
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Software aspects of MicroprocessorMachine Language, Assembly Language, Compiler, Microprocessor Programming
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Machine Language & Assembly Language Software Instruction of 1 & 0 recognized by a Microprocessor called Machine Language A software developed using mnemonics are called assembly language programs. Machine Language and Assembly language are machine dependant
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Assembly Language A low Level language arrived from the Machine Language given by a manufacturer. The language in which the mnemonics (short -hand form of instructions) used to write a program is called an Assembly Language. Assembly Language given by a Manufacturer110
Compiler A compiler converts high level program C, C +) into machine language
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Microprocessor Programming1. Assembly language-a low level language converted into machine language in Assembler 2. Machine language recognized by Microprocessor = instruction of 1 & 0 3. Assembly language and machine language is proprietary 4. Compiler converts High level language(C,C+Fortan Pascal), into machine language112
MEMORYMajor Memories, Distinction, Computer Memory,Volatile and Non Volatile memory,RAM & ROM
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TYPES OF MEMORIESMEMORIES
1. MAGNETIC
2,.OpticalCD DRIVE
3. SEMICONDUCTOR.
1.Hard Disc 2.Floppy 3.Magnetic tape
RAM
ROM114
Memories1. Magnetic Memories-Core Memory-Magnetic memories are nonvolatile memory. They store information permanently. They are slower than semiconductor memory. Three types: hard disks, floppy disks and tapes. 2. Semiconductor memories- two types: RAM (random access memory) and ROM (read only memory) 3. Optical memory-Back up memory-CD115
Core memory (Magnetic memory) Use small magnetic ceramic rings, the cores, through which wires are threaded to store information via the polarity of the magnetic field Such memory is often just called core memory Each ring stores one bit (a 0 or 1). To select a memory location, X & Y lines are driven with half the current required to cause this change.
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Core memory
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Core Memory Core Memory made up of Ferrite Cores arranged in a two-dimensional grid in X & Y Wires are threaded into X & Y thru which current is applied to change from 0 to 1 Word-lines (Rows X) Bit lines (Columns-Y)
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2.OPTICAL MEMORY-Back up1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Laser beam used to write or read an optical memory Optical memory - a back up memory Very high storage capacity. Types of optical memory are:CD-ROM, CD-R (CD Recordable), CD-RW, DVD-ROM, DVD-R and DVD-RW. CD-ROM also called compact disk ROM. Information on CDROM written at the time of manufacture. CD-ROM read-only type memory. Size of Disc 5.25 inch diameter. 650MB CD-ROMs available. Access time is 80 ms. Data transfer rate 4800KB/s. Track density 16000 tracks per inch. CD-R/W (Read/Write) of 700 MB capacity now available. A DVD-ROM is similar to CD-ROM.
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3.Magnetic memory-Non volatile1. Magnetic memories Core-nonvolatile (storing) information permanently. 2. Slower than semiconductor memory. 3. Commonly used magnetic memories: three types: hard disks, floppy disks and tapes. 4. These are bulk storage devices. 5. They store information at a lower cost compared to semiconductor devices. 6. They are rotated while reading or writing information.120
3.Semiconductor memory-Volatile1. Volatile memory storing information so long as power supply is on. 2. Two types of semiconductor memory: RAM (random access memory) and ROM (read only memory). 3. RAM is a read/write memory & ROM is a permanent type memory & cannot be written by User121
3.Semiconductor memory-Volatilecontinued3. ROM-Read only Memory: ROM contents not lost when power supply goes off. User cannot write into a ROM. ROM contents are decided by the manufacturer and written at the time of manufacture. Types of ROM are PROM, EPROM, EEPROM 4. Flash memory s electrically erasable and programmable122
Distinction between Magnetic & Semiconductor memory1. Non volatile memory 2. Bulk Storage memory & cheaper 3. High capacity available 4. Slower than 2 5. Can be read/written 6. Rotated while writing 7. Ex .Core, floppy, Cd1. Volatile memory & non volatile
2. Not a Bulk Storage memory andexpensive
3. High capacity available 4. Faster than 1 5. Either R/W or R/O6. Not rotated while writing7. Eg. RAM, ROM
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RAMRAM, types SRAM, DRAM, SDRAM.
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Memories in Digital Computer-RAM1. Internal memory ( Random Access memory) 2. Random access memory, generally called RAM the system's main memory, 3. i.e. a space that allows to temporarily store data when a program is running. 4. Unlike a hard drive, RAM is volatile=data erased when Power is switched off. 5. It only stores data as long as it supplied with electricity. Thus, each time the computer is turned off, all the data in the memory are irremediably erased.125
RAM
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Features of RAM Store a Data in either Static RAM (the state of a Flip Flop) or Dynamic RAM as a Charge in a capacitor (or transistor gate) A volatile memory RAM chips faster and compatible to motherboard. RAM often used to shadow Bios ROM to improve performance when executing BIOS code127
RAM
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Types of RAM1. S-RAM used in Cache 2. D-RAM used main memory in computer 3. SD-RAM Synchronous D Ram used in Desktop 4. C-MOS RAM for Hard disk settings 5. SVRAM-Synchronous Video RAM used in Graphics card in Multimedia.
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S-RAM S RAM-Static Random Access Memory =for Computer Speed; flip-flop holding each bit of memory;32 Ambit capacity .128 =4 chips of 32 M A CMOS Transistor memory-has 3 working states, 1.Standby,2.Reading and 3.Writing SRAM-used as General Purpose Cache, SRAM caches, hard disk buffers, router buffers, etc. LCD screens and printers for holding the image D RAM-Dynamic Random Access Memory130
Features of SRAM Characteristics -Due to a more complex internal structure, SRAM less dense than DRAM Clock rate and power -power-hungry
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D-RAM
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D-RAM Memory cells with a paired transistor and capacitor for constant refreshing DRAM mostly used in notebooks, office printers and in routers. Asynchronous D RAM( as interface), SSDRAM( in cache, in graphics adapter) and SVRAM (Buffer in Graphics)CMOS RAM ( for hard disc settings)133
ROMTYPES, PROM, EPROM, EEPROM
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ROM-Non volatile memoryIn PLC 1
PROM2
For booting
EPROM
ROM
For PC Monitor & as a Flash 3
EAPROM
FOR Parallel Computation 4
EEPROM135
ROM-Read Only Memory & types1. ROM-A DTL ;Memory Lost when supply is remote (unlike RAM) ROM-a Non volatile memory 2. PROM-programmed memory -once 3. EA PROM-Erasable Programmable memory thru an UV light 4. EEPROM Electrical Erasable PROM thru a magnetic field136
Comparison between RAM & ROM1. Primary Storage memory 2. Volatile memoryrequire power 3. All Data lost if no power 1. A firmware device for software distbn. 2. Non volatile memory-require no power 3. No data is lost
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ROM in BIOS
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Types of ROM1. PROM used in Programmable controllers, digital panel meters, vending machines, GPRS, Clutch brake controller 2. EPROM3. EAPROM-electrically alterable PROM 4. EEPROM
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PROMo PROMs (Programmable Read-Only Memory) written to (programmed) via a special device, a PROM programmer. o Writing often takes the form of permanently destroying or creating internal links (fuses or antifuses) with the result that a PROM can only be programmed once.140
2.EPROMo EPROM's (Erasable Programmable Read-Only Memory) be erased by exposure to ultraviolet light then rewritten via an EPROM programmer. Repeated exposure to ultraviolet light will eventually destroy the EPROM but it generally takes many (greater than 1000) exposures before the EPROM becomes unusable. EPROM's can be easily identified by the circular 'window' in the top which allows the UV light to enter. Once programmed, this window is typically covered by a label to prevent accidental erasure.ROM).
o
o o
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3.EAPROMo EAROMs (Electrically Alterable ReadOnly Memory) be modified a bit at a time, but writing is intended to be an infrequent operation; most of the time the memory is used as a ROM.\ o EAROM may be used to store critical system setup information in a nonvolatile way. o For many applications, EAROM has been supplanted by CMOS RAM backed-up by a lithium battery.142
4.EEPROMo EEPROM such as Flash memory (Electrically Erasable Programmable Read-Only Memory) allow the entire ROM (or selected banks of the ROM) to be electrically erased (flashed back to zero) then written to without taking them out of the computer (camera, MP3 player, etc.). o Flashing is much slower (milliseconds) than writing to RAM (nanoseconds) (or reading from any143
Flash memory Flash memory- a compromise between RAM-type memories and ROM memories Flash memory possess the non-volatility of ROM memories while providing both read and write access However, the access times of flash memories longer than the access times of RAM144