8085 Microprocessor – Assembly Language Programming (Part II)

Instruction Formats

An instruction is a binary pattern designed inside an MP to perform a specific function.

Each instruction has two parts:

• The task to be performed called the operation code (opcode).
• Data to be operated on, called the operand.

Instruction Formats Types

The instruction format is divided into three types:

• One Byte Instruction
• Two Byte Instruction
• Three Byte Instruction

One Byte Instruction

• Includes the opcode and operand in the same byte
• Operand(s) are internal register and are coded into the instruction.
• Requires one memory location.

Example of One Byte Instruction

Instruction	Opcode	Operand	HEX Code	Task
MOV C, A	MOV	C, A	4F H	Copy the content of the accumulator in register C
ADD B	ADD	B	80 H	Add the contents of registers B to the contents of the accumulator
CMA	CMA		2F H	Invert (compliment) each bit in the accumulator

Two Byte Instruction

• The first byte specifies the opcode and the second byte specifies the operand.
• The source operand is a data byte immediately following the opcode.
• The instruction would require two memory locations to store in memory.

Example of Two Byte Instruction

Instruction	Opcode	Operand	HEX Code		Task
MVI A, DATA	MVI	A, DATA	3E	First Byte	Load an 8-bit data byte in the accumulator
			DATA	Second Byte

Three Byte Instruction

• The first byte specifies the opcode, and the following two bytes specify the 16-bit address.
• The instruction would require three memory locations to store in memory.
• NOTE: The second byte is the low-order address & the third byte is the higher-order address.
• Opcode + Data Byte (LO) + Data Byte (HO)

Example of Three Byte Instruction

Instruction	Opcode	Operand	HEX Code		Task
JMP 2000 H	JMP	2000 H	C3	First Byte	Transfer the program sequence to the memory location 2000 H.
			00	Second Byte
			20	Third Byte
LDA D000 H	LDA	DOOO H	3A	First Byte	Load Accumulator with the contents from memory specify with address
			00	Second Byte
			D0	Third Byte