A CALL instruction is used to call a subroutine, while a JUMP instruction updates the program counter value and makes it point to another location inside the program. Read this article to learn more about CALL and JUMP instructions and how they are different from each other. What is a CALL Instruction? A CALL instruction is utilized to call a sub-routine. Using a CALL instruction, the program control is transferred to a location in memory that is not a part of the main program. A CALL instruction necessarily requires the initialization of a Stack Pointer (SP). It is basically ... Read More

In this section we will see how to reset the accumulator content in Intel 8085 and 8086 microprocessors.In both of the microprocessors, there are four instructions to do the work. These instructions are doing the same in both cases.Let us see the 8085 instructions first to reset the Accumulator.MnemonicsDescriptionMVI A, 00HThis instruction loads 00H into the accumulator. This is two-byte instruction.ANI 00HThis instruction performs AND operation between accumulator and 00H. This is also a two-byte instruction.XRA AThis one-byte instruction is performing the XOR operation with accumulator itself.SUB ASUB A is another one-byte instruction. It subtracts accumulator value from the accumulator. The ... Read More

These instructions are used to transfer/branch the instructions during an execution. There are two types of branching instructions. The unconditional branch and conditional branch.The Unconditional Program execution transfer instructions are as follows.OpcodeOperandDescriptionCALLaddressUsed to call a procedure and save their return address to the stack.RET----Used to return from the procedure to the main program.JMPaddressUsed to jump to the provided address to proceed to the next instruction.LOOPaddressUsed to loop a group of instructions until the condition satisfies, i.e., CX = 0 Now let us see the Conditional Program execution transfer instructions.OpcodeOperandDescriptionJCaddressUsed to jump if carry flag CY = 1JNCaddressUsed to jump if no ... Read More

String is a group of bytes/words and their memory is always allocated in a sequential order. String is either referred as byte string or word string. Here we will see some instructions which are used to manipulate the string related operations.The String manipulation instructions are as follows.OpcodeOperandDescriptionREPInstructionUsed to repeat the given instruction till CX ≠ 0.REPE/REPZInstructionUsed to repeat the given instruction until CX = 0 or zero flag ZF = 1.REPNE/REPNZInstructionUsed to repeat the given instruction until CX = 0 or zero flag ZF = 1.MOVS/MOVSB/MOVSW----Used to move the byte/word from one string to another.COMS/COMPSB/COMPSW----Used to compare two string bytes/words.INS/INSB/INSW----Used ... Read More

These instructions are used to control the processor action by setting/resetting the flag values.These are the process/processor control instructions.OpcodeOperandDescriptionSTC----Used to set carry flag CY to 1CLC----Used to clear/reset carry flag CY to 0CMC----Used to put complement at the state of carry flag CY.STD----Used to set the direction flag DF to 1CLD----Used to clear/reset the direction flag DF to 0STI----Used to set the interrupt enable flag to 1, i.e., enable INTR input.CLI----Used to clear the interrupt enable flag to 0, i.e., disable INTR input.  

These instructions are used to transfer the data from the source operand to the destination operand. These are also known as copy instructions.Let us see the data transfer instructions of 8086 microprocessor. Here the D and S are destination and source respectively. D and S can be either register, data or memory address.OpcodeOperandDescriptionMOVD, SUsed to copy the byte or word from the provided source to the provided destination.PUSHDUsed to put a word at the top of the stack.POPDUsed to get a word from the top of the stack to the provided location.PUSHA----Used to put all the registers into the stack.POPA----Used ... Read More

These instructions are used to perform operations where data bits are involved, i.e. operations like logical, shift, etc. We can say that these instructions are logical instructions. In 8086, the destination register may or may not the Accumulator.Let us see the logical instructions of 8086 microprocessor. Here the D, S and C are destination and source and count respectively. D, S and C can be either register, data or memory address.OpcodeOperandDescriptionANDD, SUsed for adding each bit in a byte/word with the corresponding bit in another byte/word.ORD, SUsed to multiply each bit in a byte/word with the corresponding bit in another ... Read More

These instructions are used to perform arithmetic operations like addition, subtraction, multiplication, division, etc. In 8086 the destination address is need not to be the accumulator.Let us see the arithmetic instructions of 8086 microprocessor. Here the D and S are destination and source respectively. D and S can be either register, data or memory address.OpcodeOperandDescriptionADDD, SUsed to add the provided byte to byte/word to word.ADCD, SUsed to add with carry.INCDUsed to increment the provided byte/word by 1.AAA----Used to adjust ASCII after addition.DAA----Used to adjust the decimal after the addition/subtraction operation.SUBD, SUsed to subtract the byte from byte/word from word.SBBD, SUsed ... Read More

In this section we will see the addressing modes of Intel 8086 microprocessor.There are eight addressing modes in 8086 MPU. These modes are:Immediate Addressing ModeRegister Addressing ModeDirect Addressing ModeRegister Indirect Addressing ModeBased Addressing ModeIndexed Addressing ModeBased-Index Addressing ModeBased-Index with displacement addressing modeImmediate AddressingThe addressing mode in which the data operand is a part of the instruction itself is known as immediate addressing mode.MOV CX, 4929 H, ADD AX, 2387 H, MOV AL, FFH  Register AddressingIt means that the register is the source of an operand for an instruction.MOV CX, AX; copies the contents of the 16-bit AX register into; the ... Read More

The flag register is one of the special purpose register. The flag bits are changed to 0 or 1 depending upon the value of result after arithmetic or logical operations.8086 has 16-bit flag register, and there are 9 valid flag bits. The format of flag register is like below.BitsD15D14D13D12D11D10D9D8D7D6D5D4D3D2D1D0Flags    ODITSZ AC P CY We can divide the flag bits into two sections. The Status Flags, and the Control Flags.Status FlagsIn 8086 there are 6 different flags which are set or reset after 8-bit or 16-bit operations. These flags and their functions are listed below.Flag BitFunctionSAfter any operation if the MSB is 1, then it indicates ... Read More