1. Instruction Formats Each instruction consists of two parts:
Opcode : specifies the operation to be performed . It is always 8 bits.
Operand : specifies the data or provides the data . It can be 8 bit or 16 bit.
OPCODE
OPERAND

2. Length of Instructions
3 - byte instruction
2- byte instruction
1-byte instruction

3. 3- Byte instruction First byte: specifies the opcode
2nd byte :specifies the operand
3rd byte : specifies the operand
These instructions use to specify the 16 bit data or memory address.
Example: STA 3000H
Move the contents of Accumulator to 3000H memory
Opcode
Operand (lower order 8 bit)
Operand (higher order 8 bit)

4. 2- Byte instruction First byte: specifies the opcode
2nd byte :specifies the operand
These instructions used to specify 8 bit data or I/O port address.
Example: MVI B, 57H
Move the data 57H to register B.
Opcode
Operand

5. 1- Byte instruction
1 –byte instruction includes the opcode and operand in the 8 bit only .
These instructions do not specify 8 bit /16 bit data/address explicitly.
Example: MOV B,C
Move the content of C register to B register.
Opcode