University of Sargodha, Lahore Campus Prepared by Ali Saeed

 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

 First Set the Environment Variable

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

 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

 and 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

 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

 In Real Addressing mode this will behaves like 8086  Program for 8086 can be executed in this mode without modifications  In protected mode 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

 It was 32 bit microprocessor  or 386 was introduced in 1985  It was much faster than having 3.3 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

 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

 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.

 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.

 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.

 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.

 CPU makes a calculation of physical address by multiplying the segment register by 10h and adding general purpose register to it (1230h * 10h + 45h = 12345h):

 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!

 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

 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

 Thanks