A two-byte instruction gives the specific function instruction in two bytes, or two words. The first specifies the opcode, which tells the microprocessor what operation will occur. The second specifies the operand, or the data that the operation is done on.
Three-byte instruction is the type of instruction in which the first 8 bits indicates the opcode and the next two bytes specify the operand.The operand may be a 16 bits address or 16 bit of data.
A 3 byte instruction is an instruction with 3 bytes, usually 1 opcode byte and 2 data bytes. Examples are LHLD 1234H, for the 8085, and MOV AX,1234H, for the 8086/8088.
What is three-byte instruction?
What is three-byte instruction?
Add
There are 74 instructions in the 8085 microprocessor.
1byte instruction = MOV A,B 2byte instruction = MVI A,01H 3byte instruction = STA 2030H
A microprocessor know whether the next byte is an instruction or data because the microprocessor knows for what it is looking. The bus, on the other hand, for an 8085 based system, knows an opcode from data by looking at S0 and S1 when IO/M- is low. If both are high, it is an opcode, otherwise it is data.
Suppose we give a 8-bit instruction ADD B to the microprocessor then this instruction is not at all understood by microprocessor as it only accepts binary inputs so first of all it stores the instruction in the INSTRUCTION REGISTOR then it decodes this instruction ADD B to its suitable binary code 80H in the INSTRUCTION DECODER.. after converting to 80H then the microprocessor understands that .. yes i have to add the content of the resistor B with that of A(accumulator) and store the result in the accumulator A this is a small example how microprocessor operates facing the instructions
The RST instruction is a 1 byte opcode with a 3 bit imbedded operand. There are 8 different RST instructions. Each pushes the PC on the stack, and loads the PC with the operand's value times 8. (0H, 8H, 10H, 18H, etc.)Pushing the PC on the stack and loading a new value into the PC is exactly what a CALL instruction does, so the RST instruction is a 1 byte CALL instruction. The difference between RST and CALL is that CALL is a 3 byte instruction which can go anywhere in memory in one instruction.
The 8085 instruction set is classified into three groups according to its Word size. They are 1. One word /1 byte instructions 2. Two word / 2 byte instructions 3. Three word / 3 byte instructions
A series of data bytes or words available in a memory at consecutive locations, to be referred to collectively or individually, are called as byte strings or word strings.
It fetches the next instruction.
branch instruction
The CALL InstructionOpcode OperandCALL 16-bit memory addressof a subroutineIt is a 3-byte instruction that transfers the program sequence to a subroutineSaves the content of the PC (Program Counter-16-bit register) , the address of the next instruction , on the stackDecrements the stack pointer register by 2Jumps unconditionally to the memory location specified by the 2nd and 3rd bytes.This instruction is accompanied by a RETURN instruction in the subroutine
The 8085 instruction set is classified into the following three groups according to word size: 1. One-word or 1-byte instructions 2. Two-word or 2-byte instructions 3. Three-word or 3-byte instructions
it goes to queue for next instruction