Chapter 4 8085 Microprocessor Architecture And Memory

Chapter 4 8085 Microprocessor Architecture And Memory Chapter 4 8085 Microprocessor Architecture and Memory This chapter delves into the intricate architecture of the 8085 microprocessor a pivotal component in the evolution of microcomputer systems We will explore its internal organization register set addressing modes and its interaction with memory Understanding these fundamentals is essential for anyone aspiring to program and utilize the 8085 effectively 41 Architecture Overview The 8085 microprocessor is an 8bit processor built with NMOS Nchannel Metal Oxide Semiconductor technology It is a singlechip device encompassing the central processing unit CPU with its internal registers arithmetic logic unit ALU control unit and associated circuitry The 8085 can address up to 65536 216 bytes of memory and communicate with external devices through its inputoutput IO ports 42 Internal Architecture 421 Registers The 8085 has a set of internal registers which act as temporary storage locations for data and program instructions These registers can be classified into different categories based on their functions General Purpose Registers 8bit A B C D E H L These registers can store and manipulate data in a variety of ways Special Function Registers 8bit Accumulator A The primary register for arithmetic and logic operations Flag Register F Stores flags representing the results of operations Program Counter PC Holds the address of the next instruction to be executed Stack Pointer SP Points to the top of the stack memory Special Function Registers 16bit HL Register Pair Consists of H and L registers combined to form a 16bit address register DE Register Pair Similar to HL DE can store a 16bit address 2 BC Register Pair Can be used as a 16bit address or to store data 422 Arithmetic Logic Unit ALU The ALU performs arithmetic and logical operations on data stored in the registers It supports functions like addition subtraction multiplication AND OR XOR and comparison 423 Control Unit The control unit manages the execution of instructions It fetches instructions from memory decodes them and directs the ALU and other components to perform the necessary operations 43 Addressing Modes Addressing modes define how the 8085 accesses data stored in memory Different modes offer flexibility and optimize program execution Immediate Addressing The data value is directly embedded within the instruction Direct Addressing The instruction contains the actual memory address of the data Register Addressing The data is stored in a specific register Indirect Addressing The instruction contains the address of a register pair which in turn holds the address of the data 44 Memory Organization The 8085 microprocessor can access up to 65536 bytes of memory organized in a linear fashion Each memory location has a unique address ranging from 0000H to FFFFh 441 Memory Segmentation The memory space is conceptually divided into three segments ROM Read Only Memory Stores the program instructions RAM Random Access Memory Used for temporary data storage and program variables IO Space Contains ports used for communication with peripheral devices 45 Instruction Set The 8085 instruction set consists of a wide array of instructions that enable the processor to perform various operations These instructions can be categorized based on their function Data Transfer Instructions Move data between registers and memory locations Arithmetic Instructions Perform arithmetic operations on data Logical Instructions Perform logical operations on data 3 Control Transfer Instructions Change the flow of program execution eg jump call return InputOutput Instructions Communicate with peripheral devices 46 Interfacing with Memory The 8085 interacts with memory through an address bus and a data bus The address bus carries the memory address to be accessed while the data bus carries the data itself The 8085 employs a memory management system to control memory access and ensure data integrity 47 Conclusion Understanding the architecture of the 8085 microprocessor is crucial for developing effective programs and applications By grasping its register set addressing modes memory organization and instruction set you can unlock the potential of this powerful yet versatile processor This knowledge provides a solid foundation for further exploration of the 8085 and related microcomputer systems Further Study The 8085 Microprocessor Architecture Programming and Interfacing by Rafiquzzaman Microprocessor Systems The 8085 Family by Ramesh S Gaonkar 8085 Microprocessor Programming Interfacing by Muhammad Ali Mazidi Exercises 1 Explain the function of each register in the 8085 2 What are the different addressing modes used by the 8085 3 Briefly describe the process of instruction execution in the 8085 4 How does the 8085 communicate with memory and IO devices 5 Write a simple program to add two numbers stored in memory locations 2000H and 2001H and store the result in location 2002H This chapter provides a foundational understanding of the 8085 microprocessors architecture This knowledge serves as a springboard for delving into more complex topics such as assembly language programming interfacing with peripherals and implementing various applications 4