COURSE OUTCOMES OF Microprocessor and programming Describe the architecture and organization of microprocessor along with instruction set format. C404.2 Describe modes and functional block diagram of 8086 along with pins and their functions C404.3 List and describe memory and addressing modes C404.4 List, describe and use different types of instructions, directives and interrupts C404.5 Develop assembly language programs using various programming tools. Visit for more Learning Resources

CHAPTER 1 Basics OF Microprocessor

Organization of A Microprocessor-based System (Computer) CPU – Central Processing Unit Memory ROM – Read Only Memory RAM – Random Access Memory I/O Keyboard Display Device Clock – Square Wave Oscillator (Timing) System Bus

Microprocessor (CPU) Programmable integrated device (silicon chip) that has computing & decision making capabilities Communicates & operates in binary numbers 0 & 1, called bits Has a fixed set of instructions in the form of binary patterns – machine language Difficult for humans to remember machine language – each instruction is represented using abbreviated names (mnemonics)

Memory Symbolic representation Word length 1 word instruction Word: no. of bits micro-P recognizes and processes at a time ( 4 - 64bit ). Instruction: combination of bit patterns with specific meaning known to micro-P. Program: Set of all instructions. address

I/O Microprocessor’s connection to the outside world Input: Keyboard, mouse Output: Monitor, printer

System Bus – wires connecting memory & I/O to microprocessor Address Bus Unidirectional Identifying peripheral or memory location Data Bus Bidirectional Transferring data Control Bus Synchronization signals Timing signals Control signal

Actions performed by microprocessor: CPU – Memory CPU – I/O Data Processing Arithmetic operations Logical operations Control Jump Interrupts

Basic Concepts of Microprocessors Differences between: Microcomputer – a computer with a microprocessor as its CPU. Includes memory, I/O etc. Microprocessor – silicon chip which includes ALU, register circuits & control circuits Microcontroller – silicon chip which includes microprocessor, memory & I/O in a single package.

Differences between: High level language Assembly language Machine language

Architecture of Intel 8085 Microprocessor

Microprocessor consists of: Intel 8085 Microprocessor Microprocessor consists of: Control unit: control microprocessor operations. ALU: performs data processing function. Registers: provide storage internal to CPU. Interrupts Internal data bus

Registers General Purpose Registers Special Purpose Registers B, C, D, E, H & L (8 bit registers) Can be used singly Or can be used as 16 bit register pairs BC, DE, HL H & L can be used as a data pointer (holds memory address) Special Purpose Registers Accumulator (8 bit register) Store 8 bit data Store the result of an operation Store 8 bit data during I/O transfer

Flag Register 8 bit register – shows the status of the microprocessor before/after an operation S (sign flag), Z (zero flag), AC (auxillary carry flag), P (parity flag) & CY (carry flag) Sign Flag Used for indicating the sign of the data in the accumulator The sign flag is set if negative (1 – negative) The sign flag is reset if positive (0 – positive) D7 D6 D5 D4 D3 D2 D1 D0 S Z X AC P CY

Zero Flag Carry Flag Is set if result obtained after an operation is 0 Is set following an increment or decrement operation of that register Carry Flag Is set if there is a carry or borrow from arithmetic operation 10110011 + 01001101 --------------- 1 00000000 1011 0101 + 0110 1100 --------------- Carry 1 0010 0001 1011 0101 - 1100 1100 --------------- Borrow 1 1110 1001

Auxillary Carry Flag Parity Flag Is set if there is a carry out of bit 3 Parity Flag Is set if parity is even Is cleared if parity is odd 1011 0101 + 0110 1100 --------------- 1 0010 0001

16 – Bit Registers Program Counter Stack Pointer A pointer to the next instruction to be executed Contains the 16-bit memory address of the next instruction Updated after processor has fetched the instruction Stack Pointer Stack – an area in memory in which temporary info is stored Stack – FILO (First In Last Out) basis Holds the address of the top of the stack

Non Programmable Registers Instruction Register & Decoder Instruction is stored in IR after fetched by processor Decoder decodes instruction in IR Internal Clock generator 3.125 MHz internally 6.25 MHz externally

Basic Working of a Microprocessor Instructions are stored sequentially in memory Microprocessor Fetches instruction from memory Decodes instruction Executes instruction

Interrupts of 8085 Microprocessor Maskable Interrupts Microprocessor can ignore or delay interrupt request INTR – General purpose interrupt RST 5.5, RST 6.5, RST 7.5 – Restart interrupts, higher priorities Nonmaskable Interrupts Enabled by default Cannot be disabled Microprocessor must respond to it immediately TRAP – highest priority

Grouping of Signals of 8085 Microprocessor Power supply and frequency signals Address bus signals Data bus signals Control and status signals Externally initiated signals & external signal acknowledgement Serial I/O port signals

Address bus signals, Data bus signals AD0-AD7, A8-A15 16 address lines – 2 sets Most significant bits (A8-A15) – single directional Least significant bits (AD0-AD7) – bidirectional Multiplexed with the bits of bi-directional data bus It is used as both address and data bus

Control and status signals Status lines: IO/M Differentiate I/O and memory applications High – I/O Low – Memory S1, S0 – status signals, to indicate the type of machine cycle in progress Control lines: RD, WR & INTA RD – data on the data bus to be read into processor WR – data on the data bus to be written to processor INTA – acknowledge an INTR interrupt _ _ _ _ _

Externally initiated signals & signal acknowledgement Reset In – reset CPU Hold – suspend CPU operation Ready – CPU go into wait state, to sync with slower devices Signal acknowledgement Reset out – high once CPU is rest HLDA – acknowledges hold signal

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