Microprocessor complete 8085, Summaries of Electrical and Electronics Engineering

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Chapter 1

Introduction to Microprocessor

Introduction

ROM RAM

I/O

interface

I/O

devices

CPU

Computer: A computer is a programmable machine that receives input, stores and

manipulates data/information, and provides output in a useful format. Basic computer system consist of a CPU, memory and I/O unit. Block diagram of a basic computer system Address bus Data bus Control bus

Block Diagram

4 Microcomputer Microprocessor Microcontroller

Definition of the Microprocessor

 Microprocessor is a Programmable, Clock driven, Register based,

Electronic device that reads instruction from a storage device, takes the

data from input unit and process the data according to the instructions

and provides the result to the output unit.

 Programmable- Perform Different set operation on the data depending on the sequence of instructions supplied by the programmer.  Clock Driven – Whole task is divided into basic operations, are divided into precise system clock periods.  Register Based – Storage element  Electronic Device – fabricated on a chip

• Memory:  Stores information such as instructions and data in binary format ( 0 and 1 ).  Sub-system” of microprocessor-based system. sub-system includes the registers inside the microprocessor.

 Read Only Memory (ROM): used to store programs that do not need

alterations.

 Random Access Memory (RAM) (R/WM) : used to store programs

that can read and altered like programs and data.

• Input/output: Communicates with the outside world.
• System Bus: Communication path between the microprocessor and peripherals.  group of wires to carry bits.

How does a Microprocessor works  To execute a program, the microprocessor “reads” each instruction from memory, “interprets” it, then “executes or perform” it.  The right name for the cycle is  Fetch  Decode  Execute  This sequence is continued until all instructions are performed.

8085 Assembly Language

 Even program is written in Hexa decimal .. It is difficult to understand.

 Program is written in mnemonic.

For E.g.: binary code 0011 1100 ( 3 C H in hexadecimal) is represented by INR

A

 INR A – INR stands for Increment, A is accumulator… this symbol suggest the operation of incrementing the accumulator by 1 Similarly 1000 0000 is equivalent ( 80 H) is represented as  ADD B– ADD stands for addition and B represents content in register B. this symbol suggest that addition of the number in register B to the accumulator content , and keep the result in A. ***So MP has 246 such bit pattern amounting to 74 different instruction for performing various operations

Chapter 2

Microprocessor Architecture & Pin

diagram

• Internal Architecture (functional block diagram)of

8085 Architecture…….cont…

8085 architecture consists of following blocks:

1. Register Array

2. ALU & Logical Group

3. Instruction decoder and machine cycle encoder, Timing and control

circuitry

4. Interrupt control Group

5. Serial I/O control Group

8085 Architecture …… cont…. (b.3) Flag Register(F): (user accessible)  8 bit Register  Indicates the status of the ALU operation.  ALU includes 5 flip flop, which are set or reset after an operation according to data conditions of the result in the accumulator. (Flag Register)

Flag Register…… cont…. Flag Significance C or CY (Carry) CY is set when an arithmetic operation generates a carry out, otherwise it is 0 (reset) P (Parity) P= 1 ; if the result of an ALU operation has an even number of 1 ’s in A; P= 0 ; if number of 1 is odd. AC (Auxiliary carry) Similar to CY, AC= 1 if there is a carry from D 3 to D 4 Bit AC= 0 if there is a no carry from D 3 to D 4 Bit (not available for user) Z(zero) Z = 1 ; if result in A is 00 H 0 otherwise S(Sign) S= 1 if D 7 bit of the A is 1 (indicate the result is - ive) S= 0 if D 7 bit of the A is 0 (indicate the result is +ive)

8085 Architecture …… cont….

(d) Pointer Register or special purpose [SP, PC]

(d.1) Stack Pointer(SP)  16 bit address which holds the address of the data present at the top of the stack memory  It is a reserved area of the memory in the RAM to store and retrieve the temporary information.  Also hold the content of PC when subroutines are used.  When there is a subroutine call or on an interrupt. ie. pushing the return address on a jump, and retrieving it after the operation is complete to come back to its original location. (d. 3 ) Program Counter(PC)  16 bit address used for the execution of program  Contain the address of the next instruction to be executed after fetching the instruction it is automatically incremented by 1.  Not much use in programming, but as an indicator to user only.

8085 Architecture …… cont….

In addition to register MP contains some latches and buffer

 Increment and decrement address latch  16 bit register  Used to increment or decrement the content of PC and SP  Address buffer  8 bit unidirectional buffer  Used to drive high order address bus(A 8 to A 15 )  When it is not used under such as reset, hold and halt etc this buffer is used tristate high order address bus.  Data/Address buffer  8 bit bi-Directional buffer  Used to drive the low order address (A 0 to A 7 ) and data (D 0 to D 7 ) bus.  Under certain conditions such as reset, hold and halt etc this buffer is used tristate low order address bus.