BAHAR DÖNEMİ MİKROİŞLEMCİLER LAB3 FÖYÜ

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INTRODUCTION OF SEGMENT A typical program on 8086 consists of at least three segments Code segment: Contains instructions that accomplish certain tasks Data segment: Stores information to be

1 INTRODUCTION OF SEGMENT A typical program on 8086 consists of at least three segments Code segment: Contains instructions that accomplish certain tasks Data segment: Stores information to be processed Stack segment: Store information temporarily What is a segment? A memory block includes up to 64KB. Why? Begins on an address evenly divisible by 16, i.e., an address looks like in XXXX0H. Offset address Location within a 64 kb segment range A range from 0000H to FFFFh Physical Address 20-bit address that is actually put on the address bus A range of 1MB from 00000H to FFFFFH Actual physical location in memory Logical Address Consists of a segment value (determines the beginning of a segment) and an offset address E.g., an instruction in the code segment has a logical address in the form of CS (code segment register):ip (instruction pointer) From logical address to physical address: Shift the segment value left one hex digit (or 4 bits) Then adding the above value to the offset address One logical -> only one physical Segment range representation Maximum 64KB logical 2500: :FFFF Physical 25000H 34FFFH ( FFFF)

Code Segment: 8086 fetches instructions from the code segment Logical address of an instruction: CS:IP Physical address is generated to retrieve this instruction from memory Data Segment: Information

2 Code Segment: 8086 fetches instructions from the code segment Logical address of an instruction: CS:IP Physical address is generated to retrieve this instruction from memory Data Segment: Information to be processed is stored in the data segment Logical address of a piece of data: DS:offset o Offset value: e.g., 0000H, 23FFH o Offset registers for data segment: BX, SI and DI Physical address is generated to retrieve data (8-bit or 16-bit) from memory Data Representation in Memory: o Memory can be logically imagine as a consecutive block of bytes How to store data whose size is larger than a byte? o Little endian: the low byte of the data goes to the low memory location o Big endian: the high byte of the data goes to the low memory location o E.g., 2738H Stack Segment A section of RAM memory used by the CPU to store information temporarily o Logical address of a piece of data: SS:SP (special applications with BP) o Most registers (except segment registers and SP) inside the CPU can be stored in the stack and brought back into the CPU from the stack using push and pop, respectively

3 Extra Segment: An extra data segment, essential for string operations o Logical address of a piece of data: ES:offset o Offset value: e.g., 0000H, 23FFH o Offset registers for data segment: BX, SI and DI In Summary, 80x86 Addressing modes: 80X86 has seven distinct addressing modes: Register o Data are held within registers o No need to access memory o E.g. MOV AX, BX Immediate o The source operand is a constant o Embedded in instructions o No need to access memory o E. g. MOV AX, 2550H Direct o Data is stored in memory and the address is given in instructions o Offset address in the data segment (DS) by default o E.g. MOV DL, [2400] Register indirect o Data is stored in memory and the address is held by a register o Offset address in the data segment (DS) by default o Registers for this purpose are SI, DI, and BX o E.g. MOV AL, [BX] Based relative o Data is stored in memory and the address can be calculated with base registers BX and BP as well as a displacement value o The default segment is data segment (DS) for BX, stack segment (SS) for BP o E.g. MOV CX, [BX]+10, Indexed relative o Data is stored in memory and the address can be calculated with index registers DI and SI as well as a displacement value

4 o The default segment is data segment (DS) o E.g. MOV DX, [SI]+5, Based indexed relative o Combines based and indexed addressing modes, one base register and one index register are used o The default segment is data segment (DS) for BX, stack segment (SS) for BP o E.g. MOV CL, [BX][DI]+8, ASSEMBLY LANGUAGE PROGRAMMING Model definition Used to select the size of the memory model o. MODEL SMALL: Most widely used memory models Is sufficient for the lab programs Uses a maximum of 64kb of memory for code and another 64kb for data o. MODEL MEDIUM Data must fit into 64 kb but the code can exceed o. MODEL COMPACT Data can exceed 64 kb but the code cannot exceed o. MODEL LARGE Data and code can exceed 64 kb but no single set of data should exceed 64 kb o. MODEL HUGE

5 Data and code can exceed 64 kb data can exceed o. MODEL TINY Used with COM files, data and code must fit into 64kb SEGMENT OF A PROGRAM An assembly language program can be written only in one segment. Normally a program consist of at least three segments.stack: Defines the beginning of the stack segment o.stack 64: reserves 64 byte of memory for the stack.data: Defines the beginning of the data segment o.data DATA1 DB 52H.CODE: Defines the beginning of the code segment o.code MOV load the data segment address MOV DS, AX. LABROTORY PRELIMINARY: 1. Assume that the register have the following values CS= 1000h, DS=3000h, SS= 2000h SI=5000h, DI= 4000h, BX=7000h, BP=6800h, AX=15F0h, CX=7819h and DX=1190h calculate the physical address of memory where the operand is stored and the content of the memory location in each of the following addressing examples MOV [SI], AL MOV [SI+BX+8], AH MOV [BX], AX MOV [DI+6], BX MOV [BP][SI]+10, DX 2. Convert the following code to three segments assembly program. ORG 100H MOV AX,1F16H MOV BH, AH MOV CX, AX; MOV [1004H],AX MOV AX, [BX] MOV AX, [0000H] MOV CL, 'A' MOV AX, DATA MOV DS, AX RET DATA DB 1,2,3,4,5 ; Insert code here

6 3. What are the meaning of infix, postfix and prefix? How do you use stack while calculating them?

CC411: Introduction To Microprocessors

CC411: Introduction To Microprocessors OBJECTIVES this chapter enables the student to: Describe the Intel family of microprocessors from 8085 to Pentium. In terms of bus size, physical memory & special