SKYSPIN
The 1st part of an instruction which specifies the task to be performed by the computer is called Opcode.
The 2nd part of the instruction is the data to be operated on, and it is called Operand. The Operand (or data) given in the instruction may be in various forms such as 8-bit or 16-bit data, 8-bit or 16-bit address, internal registers or a register or memory location.
According to the word size, the Intel 8085 instructions are classified into the following three types:
2. Two-byte instruction: In a two byte instruction the first byte of the instruction is its opcode and the second byte is either data or address.
Example:
MVI B, 05; 05 moved to register B.
06, 05; MVI B, 05 is in the code form.
The first byte 06 is the opcode for MVI B and second byte 05 is the data which is to be moved to register B.
3. Three-byte instruction: The first byte of the instruction is its opcode and the second and third bytes are either 16-bit data or 16-bit address.
Example:
LXI H, 2400H; Load H-L Pair with 2400H
21, 00, 24; LXI H, 2400H in the code form
The first byte 21 is the opcode for the instruction LXI H. The second 00 is 8 LSBs of the data (2400H), which is loaded into register L. The third byte 24 is 8 MSBs of the data (2400H), which is loaded into register H.
8085 Instructions
An instruction of computer is a command given to the computer to perform a specified operation on given data. Some instructions of Intel 8085 microprocessor are: MOV, MVI, LDA, STA, ADD, SUB, RAL, INR, MVI, etc.Opcode and Operands
Each instruction contains two parts: Opcode (Operation code) and Operand.The 1st part of an instruction which specifies the task to be performed by the computer is called Opcode.
The 2nd part of the instruction is the data to be operated on, and it is called Operand. The Operand (or data) given in the instruction may be in various forms such as 8-bit or 16-bit data, 8-bit or 16-bit address, internal registers or a register or memory location.
Instruction Word Size
A digital computer understands instruction written in binary codes (machine codes). The binary codes of all instructions are not of the same length.According to the word size, the Intel 8085 instructions are classified into the following three types:
- One byte instruction
- Two byte instruction
- Three byte instruction
- MOV A, B - Move the content of the register B to register A.
- ADD B ? Add the content of register B to the content of the accumulator.
2. Two-byte instruction: In a two byte instruction the first byte of the instruction is its opcode and the second byte is either data or address.
Example:
MVI B, 05; 05 moved to register B.
06, 05; MVI B, 05 is in the code form.
The first byte 06 is the opcode for MVI B and second byte 05 is the data which is to be moved to register B.
3. Three-byte instruction: The first byte of the instruction is its opcode and the second and third bytes are either 16-bit data or 16-bit address.
Example:
LXI H, 2400H; Load H-L Pair with 2400H
21, 00, 24; LXI H, 2400H in the code form
The first byte 21 is the opcode for the instruction LXI H. The second 00 is 8 LSBs of the data (2400H), which is loaded into register L. The third byte 24 is 8 MSBs of the data (2400H), which is loaded into register H.
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