Computer Organization & Assembly Language

1. Computer Organization & Assembly Language University of Sargodha, Lahore Campus Prepared by Ali Saeed

2. What is MASM • MASM stands for Microsoft Macro Assembler • The Microsoft Macro Assembler is an x86 assembler that uses the Intel syntax for MS-DOS and Microsoft Windows

3. How to use MASM • First Set the Environment Variable

4. How to use MASM

5. How to use MASM • Edit Command is use to enter in Assembly Editor • MASM prog1.asm to Compile • Link prog1 • Prog1; to run

6. 8086 and 8088 Microprocessor • 8086 was introduced in 1978 • It had 16 bit processor • 8088 was introduced in 1979 • 8088 has 8 bit data bus • 8086 has faster clock rate, thus batter performance • 8088 is less expensive

7. 80186 and 80188 Microprocessor • 80186 and 80188 are enhanced versions of 8086 and 8088 respectively • These has new instruction set called extended instruction set • But, these did not had significant advantages over 8086 and 8088 • Soon it was replaced by 80286

8. 80286 Microprocessor • It was introduced in 1982 • It was also 16 bit processor • It was faster then 8086 (12.5 MHz Vs 10MHz) • It has two number of operation modes • Real Addressing Mode • Protected virtual Addressing Mode

9. 80286 Microprocessor • In Real Addressing mode this will behaves like 8086 • Program for 8086 can be executed in this mode without modifications • In protected mode 80286 support multitasking, ability to execute several tasks at a time • Memory protection in protected mode memory use by one program can’t be use by others

10. 80386 and 80386SX Microprocessor • It was 32 bit microprocessor • 80386 or 386 was introduced in 1985 • It was much faster than 80286 having 33 MHz Processor • It has three modes • Real Addressing Mode • Protected virtual Addressing Mode • Virtual 8086 mode (run multiple 8086 application under memory protection mode) • 386XS has same internal structure as 386, but has 16 bit bus

11. What is Register • Registers are small memory area inside the CPU. • Registers have fastest speed then other memory devices i.e. RAM, Hard Disk etc… • Registers are available of different size • 8 bit • 16 bit • 32 bit

12. 8086 Register

13. Organization of Registers in x86

14. Registers • Intel 8086 had 14 registers • 4 registers are general purpose registers (AX, BX, CX, DX) • 4 Registers are known as Segment Registers • 4 registers are Index/ Pointer Register (SP, BP, SI, DI) • 2 are special purpose registers IP and Flag, user cant move directly data in it

15. Registers • AX - the accumulator register (divided into AH / AL). • BX - the base address register (divided into BH / BL). • CX - the count register (divided into CH / CL). • DX - the data register (divided into DH / DL). • SI - source index register. • DI - destination index register. • BP - base pointer. • SP - stack pointer.

16. Segment Registers • Segment Register is a way to access more then 216 (65536) (64 K) memory. • Each segment is identified by a number called segment number. (Segment 1, Segmen2, Segment 3…) • Address bit was 20 bit, it use 2 registers

17. Segment Registers • CS - points at the segment containing the current program. • DS - generally points at segment where variables are defined. • ES - extra segment register, it's up to a coder to define its usage. • SS - points at the segment containing the stack.

18. Segment Registers • Although it is possible to store any data in the segment registers • This is never a good idea. • The segment registers have a very special purpose - pointing at accessible blocks of memory. • Segment registers work together with general purpose register to access any memory value.

19. Segment Registers • For example if we would like to access memory at the physical address 12345h (hexadecimal), we should set the DS = 1230h and SI = 0045h. • This is good, since this way we can access much more memory than with a single register that is limited to 16 bit values.

20. Segment Registers • CPU makes a calculation of physical address by multiplying the segment register by 10h and adding general purpose register to it • Physical Address= Segment * 10H + Offset • (1230h * 10h + 45h = 12345h):

21. Segment Registers • The address formed with 2 registers is called an effective address. • By default BX, SI and DI registers work with DS segment register; • BP and SP work with SS segment register. • Other general purpose registers cannot form an effective address! • Also, although BX can form an effective address, BH and BL cannot!

22. Pointer and Index Register • SP – Stack Pointer, it is use to conjunction with SS to access the stack segment • BP – Base Pointer, it is used primarily to access data on stack, but unlike SP we can use BP to access data in other segment • SI – Source Index, it is used to point memory location in data segment address by DS. By adding SI we can easily access consecutive memory locations • DI – Destination Index, it work like SI, It work with string operations, and access memory with ES

23. Instruction Pointer (IP) • All register come above is for data register. • To access instructions 8086 use registers CS and IP. • CS contain the segment number of next instruction • IP contain offset of next instruction • IP is updated every time as each instruction is executed • IP can not be manipulated by an instruction • An instruction may not contain IP as operand

24. Thanks