In 8085 Instruction set, ADD R is a mnemonic that stands for “Add contents of R to Accumulator”. As addition is a binary operation, so it requires two operands to be operated on. So input operands will reside on Accumulator and R registers and after addition the result will be stored back on to Accumulator. In this case, “R” stands for any of the following registers or memory location M pointed by HL pair. R = A, B, C, D, E, H, L, or M It is 1-Byte instruction so occupies only 1-Byte in memory. As R can ... Read More

In 8085 Instruction set, SHLD is a mnemonic, which stands for Store HLpair using Direct addressing in memory location whose 16-bit address is denoted as a16. As HL pair has to be stored, so it has to be stored in two consecutive locations starting at the address a16. We know that H and L are 8-bit registers. So their contents will be stored in two consecutive memory locations as each memory location can hold 8-bits of data. This instruction uses absolute addressing mode for specifying the destination. It occupies 3-Bytes in the memory. Mnemonics, Operand Opcode(in HEX) Bytes ... Read More

In 8085 Instruction set LHLD is a mnemonic that stands for Load HL pair using Direct addressing from memory location whose 16-bit address is denoted as a16. So the previous content of HL register pair will get updated with the new 16-bits value. As HL pair has to be updated, so data comes from two consecutive memory locations starting at the address a16 and also from next address location. This instruction uses absolute addressing mode for specifying the data in the instruction. It occupies 3-Bytes in the memory. Mnemonics, Operand Opcode(in HEX) Bytes LHLD Address 2A ... Read More

In 8085 Instruction set, STAX is a mnemonic that stands for SToreAccumulator contents in memory pointed by eXtended register denoted as “rp”.Hererp stands for register pair. This instruction uses register indirect addressing for specifying the destination. So using this instruction, the current content of Accumulator will be written to the memory location as pointed by 16-bit address as stored in the register pair. It occupies only 1-Byte in memory. Mnemonics, Operand Opcode(in HEX) Bytes STAX B 02 1 STAX D 12 1 STAX B is an example instruction of this type. It ... Read More

In 8085 Instruction set, LDAX is a mnemonic that stands for LoaD Accumulator from memory pointed by eXtended register pair denoted as “rp” in the instruction. This instruction uses register indirect addressing for specifying the data. It occupies only 1-Byte in the memory. This rp can be either BC register pair represented by B or DE register pair represented by D.Note that LDAX H is not provided in 8085 instruction set. This is because, LDAX H is the same as MOV A, M in its function. Mnemonics, Operand Opcode(in HEX) Bytes LDAX B 0A 1 ... Read More

In 8085 Instruction set, there is one mnemonic XCHG, which stands for eXCHanGe. This is an instruction to exchange contents of HL register pair with DE register pair. This instruction uses implied addressing mode. As it is1-Byte instruction, so It occupies only 1-Byte in the memory. After execution of this instruction, the content between H and D registers and L and E registers will get swapped respectively. Mnemonics, Operand Opcode(in HEX) Bytes XCHG EB 1 Let us suppose, HL and DE register pairs are having ABCDH and 6789H contents respectively. After execution of ... Read More

In 8085 Instruction set, STA is a mnemonic that stands for STore Accumulator contents in memory. In this instruction, Accumulator8-bit content will be stored to a memory location whose 16-bit address is indicated in the instruction as a16. This instruction uses absolute addressing for specifying the destination. This instruction occupies 3-Bytes of memory. First Byte is required for the opcode, and next successive 2-Bytes provide the 16-bit address divided into 8-bits each consecutively. Mnemonics, Operand Opcode(in HEX) Bytes STA Address 32 3 Let us consider STA 4050H as an example instruction of this type. ... Read More

In 8085 Instruction set, LDA is a mnemonic that stands for LoaD Accumulator with the contents from memory. In this instructionAccumulatorwill get initialized with 8-bit content from the 16-bit memory address as indicated in the instruction as a16. This instruction uses absolute addressing for specifying the data. It occupies 3-Bytes in the memory. First Byte specifies the opcode, and the successive 2-Bytes provide the 16-bit address, i.e. 1-Byte each for each memory location. Mnemonics, Operand Opcode(in HEX) Bytes LDA Address 3A 3 Let us consider LDA 4050H as an example instruction of this type. ... Read More

In 8085 Instruction set, this instruction MVI M, d8 is used to load a memory location pointed by HL pair with an 8-bit value directly. This instruction uses immediate addressing for specifying the data. It occupies 2-Bytes in memory. Mnemonics, Operand Opcode(in HEX) Bytes MVI M, Data 36 2 As an example, we can consider MVI M, ABH as an example instruction of this type. It is a 2-Byte instruction, with opcode for MVI M using up one Byte, and ABH using up another more Byte. We are considering that HL register pair is ... Read More

In the 8085 Instruction set there are four instructions, which belong to the type LXI rp, d16. These instructions are used to load the 16-bit address into the register pair. We can use this instruction to load data from memory location using the memory address, which is stored in the register pair rp. For an example, if the instruction is LXI H, FE50. It means that the FE50 is loaded into the HL register pair. The rp can be BC, DE, HL or SP. The LXI instructions and their Hex-codes are as follows. Mnemonics, Operand Opcode (in HEX) ... Read More