Summary of programming workflow

Intro to 8086 Assembly Language

8086 Microprocessor Architecture

8086 is a 16-bit machine, which means that the data bus size is 16 bits; registers of the CPU have a size of 16 bits too. The address bus size is 20 bits.

Introduced	1978
Clock speeds	5MHz, 8MHz, 10 MHz
Bus width	16 bits
Number fo transistors	29,000
Feature size	3 mm
Addressable memory	1 MB

Registers of the 8086 microprocessor:

General register

AX	Accumulator
BX	Base
CX	Count
DX	Data

Pointers & index

SP	Stack pointer
BP	Base pointer
SI	Source index
DI	Destination index

Segment

CS	Code
DS	Data
SS	Stack
ES	Extract

Program status

IP	Instruction pointer
	Flags

8086 Memory Byte Ordering

8086’s endianess is little endian

8086 Stack implementation

Program Status Word Registers

When a flag is set it has a value of 1, reset value is 0.

The flag are in the PSW (Program Status Word) 16-bit registers

Status Flags

• Sign (SF): Contains the sign bit of the result of the last arithmetic operation.
• Zero (ZF): Set when the result of the operation is 0.
• Carry (CF): Set if an operation resulted in a carry (addition) in or borrow (substraction) out of a higher order bit. Used for multiword arithmetic operations.
• Auxiliary carry (AF): set when some arithmetic operations generat carry after the lower half & sends it to the upper half.
• Parity (PF): Odd parity, so: set when result has even number of 1s; otherwise 0 for odd number of 1s.
• Equal : Set if a logical compare result is equality.
• Overflow (OF): Used to indicate arithmetic overflow.

Control Flags

• Interrupt Enable/Disable (IF): Used to enable or disable interrupts
• Supervisor : Indicates whether the processor is executing in supervisor or user mode. Certain privileged instructions or areas of memory can be executed/accessed only in supervisor mode.

Format of Assembly Instructions

Type of Assembly Language Statements

8086 Addressing Modes

8086 Array Declaration

Main Instructions

Data Transfer Opcodes

Flow Control Opcodes

Branch (or jump) Instructions

Arithmetic Opcodes

Bit Manipulation Opcodes

Boolean Logic Instructions

Shift & Rotate Instructions

Multiply by a generic constant

Example

.text
main:
    mov AX 15h