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Lecture 8 Presented By Dr. Shazzad Hosain Asst. Prof. EECS, NSU
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What is Microcomputer?
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Typical Microcomputer Architecture
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The Microcomputer Bus Address Bus – Information transfer one direction, microprocessor to memory or I/O elements, so unidirectional bus – Typically 20 to 32 bit long – Determines addressable memory, 1 MB to 4 GB
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The Microcomputer Bus Data Bus – Bidirectional i.e. to or from microprocessor – Multiplexed / time shared data bus e.g. in 8086 20 bit address is send through 16-bit data bus and 4 status lines – Determines the word size of the microcomputer Control Bus – Used to send control signals to synchronize the operation of individual microcomputer elements – Each microcomputer has a unique set of control signals.
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Clock Signals Clock generator generates clock signals Most MPs have external clock generator circuit Each instruction requires a number of clock signals Clock signals determines the speed of MPs The short period cycle means clock speed is large, means high speed of computer
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The single chip microprocessor Microprocessor is the CPU of the microcomputer The main areas of microprocessor – Register section – The control unit – The arithmetic and logic unit (ALU)
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Basic Microprocessor Registers Instruction Register (IR): stores instructions Program Counter (PC): contains the address of the next instruction to be executed Memory Address Register (MAR): contains address of data Accumulator (A): typically a 8 bit register, used to store result after most ALU operations
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Accumulator based vs. general purpose based microprocessor Accumulator based – Intel 8085 and Motorola 6809 are accumulator based. – Accumulator is used as one of the data source – Result goes to accumulator – Example: ADD R1 General purpose based – Intel 8066/../Pentium are of this kind. – The registers contain hold data, memory address, results of ALU so on. – Example: ADD AX, BX, ADD [AX], BX
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Use of the Basic Microprocessor Registers Let us add contents of two memory locations For example, add [2010] = 0002 and [2012] = 005 In general [NNNN] represents the content of the memory location NNNN.
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Steps of Addition of [2010]+[2012] Load MAR with 2010 Move contents of 2010 into data register, D0, which may be AX/BX etc. Increment MAR by 2 to hold 2012 Add D0 with [2012] and store the result into D0 Instruction set form Motorola 68000
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PC L E L E L E L E
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Microprogramming the Control Unit Each instruction is executed by a set of microinstructions The microinstructions has their own codes The codes are stored into internal memory, called the control memory (ROM) Let us increment a register by 1
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Assembly Language Instruction Format Three address Two address One address Zero address CLD; clear direction NOP; No operation For all microprocessors
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References Chapter 6, Fundamental of Digital Logic and Microcomputer Design – by M. Rafiquzzaman – 6.1, 6.2, 6.3, 6.6.3
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