The 8088 and 8086 Microprocessors,Triebel and Singh 5 6.1 Flag Control Instructions- Loading and Storing the Flags Register • Format of the flags in the AH register •All loads and stores of flags take place through the AH register •B0 = CF •B2 = PF •B4 = AF •B6 = ZF •B7 = SF • Load the AH register with the content of the flags registers LAHF The AAA instruction can be used after addition to get the current result in unpacked BCD form. The OP CODE and addressing mode designation may be 1 to 2 byte. The logical group includes AND, OR, XOR, NOT, and TEST instructions. We review their content and use your feedback to keep the quality high. The Arithmetic Instructions in 8086 allows you to add the ASCII codes for two decimal digits without masking off the "3" in the upper nibble of each digit. It is 16-bit wide with a collection of 1-bit values that indicates the current state of the execution of arithmetic or logical instruction in the processor. The source can be a register, a memory location, or an immediate number. The instructions in 8086 are 1 to 7 byte long depending on the addressing mode. Counter (CX) Register → In rotate and shift instructions, register CL is used as 8 bit counter i.e., it used to store 8-bit count. The 8086 has four groups of the user accessible internal registers. the second operand can be an immediate number, a register, or a memory location. Who are the experts? 8086 Microprocessor Data Transfer Instructions. The Arithmetic Instructions in 8086 allows you to add the ASCII codes for two decimal digits without masking off the "3" in the upper nibble of each digit. Base (BX) Register → For reading data from memory or writing data into memory, 8086 microprocessor has to select one memory location, 16-bit effective address of this memory location can be stored in register BX. ROL Instruction : This instruction stands for Rotate Left without carry flag. MOV Instruction. There are 4 segment registers in 8086 Microprocessor and each of them is of 16 bit. 8086 assembly language MOV instruction is a data transfer instruction that copies a byte or word data from a specified source (second operand) to a specified destination (first operand). Instruction Set of 8086 Instructions are classified on the basis of functions they perform. Instruction Register and Instruction Decoder: The EU fetches an opcode from the queue into the instruction register. The contents of the operand (register or memory location) are rotated left bit-wise by some number of positions depending on the count value. The Flag register is a Special Purpose Register. STOSB instruction in 8086: The STOS instruction copies a byte from AL or a word from AX to a memory location in the extra segment. 8086 ADD Instruction Edit. In 80386 and the latest versions, the size of this register is extended to 32-bits and is known as the EIP register. AX - This is the accumulator. It is 16-bit registers, but it is divided into two 8-bit registers. After the copy, DI is automatically incremented or . To get the loop instruction to work first you have to define a label, set the value in cx which would be the number of times the loop should execute. What it means is that there are no instructions by which the programmer can load it with values of his choice. They are, Rotate Instructions. Flag/Status register (16 bits): It has 9 flags that help change or recognize the state of the microprocessor. The instruction register The 8086, like most processors, has an instruction register that holds the instruction that is currently being executed. The instruction register feeds the instruction to the "group decode ROM". String is series of bytes or series of words stored in sequential memory locations. the second operand can be an immediate number, a register, or a memory location. There are 8 general purpose registers in 8086 microprocessor. 8086 INSTRUCTION SET DATA TRANSFER INSTRUCTIONS MOV - MOV Destination, Source The MOV instruction copies a word or byte of data from a specified source to a specified destination. 6 Status flags: In the 8086, the instruction register holds the first byte of an instruction (which may consist of multiple bytes), so it is built from eight latches (below). Algorithm: shift all bits left, the bit that goes off is set to CF and previous value of CF is inserted to the right-most position. The MOV instruction does not affect any value in the flag register. Register Function; AX: This is the accumulator. Flag register of 8086 microprocessor. We know that instructions are the binary commands used for the execution of any operation. Example Assembly Code Only the microprocessor's compiler can do this. In the previous article, we have discussed the instruction set of the 8085 microprocessor.Here in this article, we will discuss the instruction set supported by the 8086 microprocessor.. 8086 supports various instructions including those supported by 8085. x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit version of the x86 instruction set, first released in 1999.It introduced two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level paging mode.. With 64-bit mode and the new paging mode, it supports vastly larger amounts of virtual memory and physical memory than was possible on its 32-bit . The instruction decoder decodes it and sends the information to the control circuit for execution. General purpose registers are used to store temporary data within the microprocessor. The code and instructions are stored inside these different segments. The source can be a register, a memory location or an immediate number. The 8086 MOV instruction supports the following operands: The instruction MOV mem, mem is illegal. 2) Segment Registers. It is of 16 bits and is divided into two 8-bit registers BH and BL to also perform 8-bit instructions. Four of them, AX, BX, CX, DX, can also be accessed as twice as many 8-bit registers (see figure) while the other four, SI, DI, BP, SP, are 16-bit only. This ROM determines the high-level characteristics of the instruction, such as if it is a single-byte instruction, a multi-byte instruction, or an instruction prefix. It is not possible to transfer data directly from one memory location to another. Some instructions specify registers as part of the instruction.1 8086 16bit Registers inside cpu very fast no address no type only length of bits . Let us learn briefly about rotate instructions of the 8086 microprocessor. Figure - General purpose registers. All of these instructions are discussed in detail. The description of these general purpose registers Depending upon the value of result after any arithmetic and logical operation the flag bits become set (1) or reset (0). The immediate byte may be 8 or 16 bit, and the displacement in an instruction can be 0 bits or 8 bits or 16 bits. In the instruction, ADD [AX], BX, the content of memory location of BX register is added with AX register and the result is stored in the AX register. Shift and Rotate Instructions in 8086 Microprocessor In this article, we are going to study another type of instructions of the 8086 microprocessor which are used for shifting or rotating the contents of the register. DI is used to hold the offset of the memory location in the extra segment. Experts are tested by Chegg as specialists in their subject area. The AAA instruction can be used after addition to get the current result in unpacked BCD form. STOSB instruction in 8086: The STOS instruction copies a byte from AL or a word from AX to a memory location in the extra segment. Data Segment Register (DS): The data, variables and constants given in the program are held in the data segment of the memory. 1 point AX BX Ο Ο Ο CX DX What is the length of address bus of 8086 microprocessor? The instruction register feeds the instruction to the "group decode ROM". Murugan Andezuthu Dharmaratnam | 13 February 2021 | 927 Add is an arithmetic instruction that adds the second operand with the first and stores the result in the first operand. & the first operand also can be a general-purpose register or . 8086 Microprocessor Data Transfer Instructions. String Instructions. The 8086 microprocessor supports 8 types of instructions − Data Transfer Instructions Arithmetic Instructions Bit Manipulation Instructions String Instructions Program Execution Transfer Instructions (Branch & Loop Instructions) Processor Control Instructions Iteration Control Instructions Interrupt Instructions (a) Status Flags - There are 6 flag registers in 8086 microprocessor which become set (1) or reset (0) depending upon condition after . Let us learn briefly about rotate instructions of the 8086 microprocessor. The 8086 has a total of fourteen 16-bit registers including a 16 bit register called the status register, with 9 of bits implemented for status and control flags. While the shift instructions group includes SHR, SHL, SAR, and SAL instructions, and rotate instructions include ROL, ROR, RCR, and RCL . Immediate mode instructions have only one register or memory operand; the other is encoded in the instruction itself The Reg field is used an "opcode extension" The addressing mode byte has to be examined to determine which operation is specified add imm to reg/mem 1000 00sw mod000r/m Four of them, AX, BX, CX, DX, can also be accessed as twice as many 8-bit registers (see figure) while the other four, SI, DI, BP, SP, are 16-bit only. General purpose registers in 8086 microprocessor General purpose registers in 8086 microprocessor Microprocessor Microcontroller 8086 The general purpose registers are used to store temporary data in the time of different operations in microprocessor. Microprocessor - 8086 Instruction Sets, The 8086 microprocessor supports 8 types of instructions − . Out of 16 bits, 9 bits are used in the 8086 as shown below. 8086 ADD Instruction Edit. The destination can be a register or a memory location. It checks the AL register and then take following actions: 1. In 8086 microprocessor instruction set, the bit manipulation instructions are divided into three groups. POPF − Used to copy a word at the top of the stack to the flag register. IR (Instruction Register) is a special purpose register, which is used to receive the 8-bit opcode portion of an instruction. This ROM determines the high-level characteristics of the instruction, such as if it is a single-byte instruction, a multi-byte instruction, or an instruction prefix. The flag register of 8086 is a flip-flop. Example: ADD AX, AX (AX = AX + AX) BX - This is the base register. The contents of the operand (register or memory location) are rotated left bit-wise by some number of positions depending on the count value. (This is only a piece of the 8086's complex instruction handling. It checks the AL register and then take following actions: 1. Instruction register (IR) in 8085 Microprocessor. DI is used to hold the offset of the memory location in the extra segment. These instructions are used to perform arithmetic operations like addition, subtraction, multiplication, division, etc. ADC (Add with carry) For 32 bit addition in 8086 processor can be done by adding the LSB sides at first and with the carry, the remaining MSB is adder4. ROL Instruction : This instruction stands for Rotate Left without carry flag. MOV Instruction. It is not accessible to the programmer. The source can be value, general-purpose register or a memory location. The destination can be a register or a memory location. The nine active flags are divided into two groups namely status flags and control flags. Where the OPCODE use 2 byte, the first byte is OPCODE and the . All of these instructions are discussed in detail. (This is only a piece of the 8086's complex instruction handling. When immediate is greater then 1, assembler generates several RCL xx, 1 instructions because 8086 has machine code only for this instruction (the same principle works for all other shift/rotate instructions). Arithmetic Instructions. 8086 has eight general purpose registers. A register may hold an instruction, a storage address, or any kind of data (such as a bit sequence or individual characters). & the first operand also can be a general-purpose register or . Murugan Andezuthu Dharmaratnam | 13 February 2021 | 927 Add is an arithmetic instruction that adds the second operand with the first and stores the result in the first operand. The source can be a register, a memory location, or an immediate number. In the instruction, ADD [AX], BX, the content of memory location of BX register is added with AX register and the result is stored in the AX register. There are 4 segment registers in 8086 as given below: Code Segment Register (CS): Code segment of the memory holds instruction codes of a program. The MOV instruction data transfers a data or word from source to destination. Example: 1. Therefore, both source and destination operands cannot be memory address. Converting Assembly Language Instructions to Machine Code • An instruction can be coded with 1 to 6 bytes • Byte 1 contains three kinds of information - Opcode field (6 bits) specifies the operation (add, subtract, move) - Register Direction Bit (D bit) Tells the register operand in REG field in byte 2 is source or destination operand The MOV instruction data transfers a data or word from source to destination. 8086 assembly language loop instruction. Code Segment (CS) Register: The user cannot modify the content of these registers. In the 8086 Microprocessor, the registers are categorized into mainly four types: General Purpose Registers Segment Registers Pointers and Index Registers Flag or Status Register 1) General Purpose Registers The use of general-purpose registers is to store temporary data. The following instructions come under this category: Instruction. 8086 Instruction Format-I. 8086 Instruction Encoding-15 Immediate Operand Instructions! 1 point 8 bit 16 . They are categorized into the following main types: Data Transfer instruction All the instructions which perform data movement come under this category. ADC (Add with carry) For 32 bit addition in 8086 processor can be done by adding the LSB sides at first and with the carry, the remaining MSB is adder4. The 8086 has eight more or less general 16-bit registers (including the stack pointer but excluding the instruction pointer, flag register and segment registers). Instruction pointer values get incremented automatically after every instruction is executed. The 8086 provides some instructions which handle string operations such as string movement, comparison, scan, load and store. It is generally used for arithmetical and logical instructions but in 8086 microprocessor it is not mandatory to have accumulator as the destination operand. 1. a loop instruction is used to loop a group of instructions until the condition satisfies, i.e., CX = 0. This instruction copies the contents of lower byte of 8086 flag register to AH register. These registers are AH and AL. The destination can be a register or a memory location. The 8086 has eight more or less general 16-bit registers (including the stack pointer but excluding the instruction pointer, flag register and segment registers). Transcribed image text: Which register is used as an iterator of LOOP instructions? This instruction copies the contents of lower byte of 8086 flag register to AH register. A processor register (CPU register) is one of a small set of data holding places that are part of the computer processor. They are the instruction pointer, four data registers, four pointer and index register, four segment registers. AX generally used for arithmetic or logical instructions, but it is not mandatory in 8086. It is of 16 bits and is divided into two 8-bit registers AH and AL to also perform 8-bit instructions. 8086 MOV Instruction. The IP register is a 16-bit register which contains the address of the next instruction to be executed. We will first discuss the working of each of these instructions and will then also discuss the syntax for each of them.
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