MOV AX, AX := m Based-Index Indirect with Displacement. Mov ax,(si)Īssembly language registers, MOV AX, AX := m. Destination operand can never be immediate data. MOV AX, BX XOR AX, DX ADD AL, BL Immediate mode – In this type of addressing mode the source operand is a 8 bit or 16 bit data. The operand between the brackets is treated as an address and the value at that memory address if fetched. mov ax, bx mov ax, If bx contains the value 100h and the value at memory address 100h is 23, does the second one copy 23 to ax? Also, what is the difference between the two following lines? mov ax, 102h moves value of 102h into register ax mov ax, Actual address is DS:0 + 102h Instruction Set, examples: mov ax,bx mov ax,10h mov si,es: Direct Memory Addressing A memory location can be used by using its address as the operand in an instruction. (Order of dest and src MOV AX,, MOV AL, Register indirect addressing mode This addressing mode allows data to be addressed at any memory location through an offset address held in any of the following registers: BP, BX, DI & SI. Instructions with two operands : destination (dest), source (src). |INT |immediate byte |Interrupt numbered by immediate byte (0.255).CONCEPT OF MOV AX,CS and MOV DS,AX Mov ax, bx | | |IN AL, 7 get status of stepper-motor. | | |IN AX, 4 get status of traffic lights.
| |AX, im.byte |access port number over 255 - DX register should | | |AL, DX |Second operand is a port number. |IN |AL, im.byte |Input from port into AL or AX. | | |Corrects the result of subtraction of two packed | |DAS |No operands |Decimal adjust After Subtraction. | | |Corrects the result of addition of two packed BCD | |DAA |No operands |Decimal adjust After Addition. |CWD |No operands |Convert Word to Double word. |CMPSW |No operands |Compare words: ES: from DS. | | |������ set flags according to result: | |CMPSB |No operands |Compare bytes: ES: from DS. | | |CMP AL, BL AL = 5, ZF = 1 (so equal!) | | |REG, immediate |set (OF, SF, ZF, AF, PF, CF) according to | | |memory, immediate |result is not stored anywhere, flags are | |CMC |No operands |Complement Carry flag. |CLI |No operands |Clear Interrupt enable flag. | | |by chain instructions: CMPSB, CMPSW, LODSB, | |CBW |No operands |Convert byte into word. | | |Call, so CS is also pushed to stack). | |4-byte address |entered in this form: 1234h:5678h, first value is segment second value is an offset (this | |CALL |procedure name |Transfers control to procedure, return address is | | |memory, REG |Result is stored in operand1. |AND |REG, memory |Logical AND between all bits of two operands. | |REG, REG |operand1 = operand1 + operand2 | | |REG, REG |operand1 = operand1 + operand2 + CF | | | |Corrects result in AH and AL after subtraction | |AAS |No operands |ASCII Adjust after Subtraction. | | |Corrects the result of multiplication of two BCD | |AAM |No operands |ASCII Adjust after Multiplication. | | |Prepares two BCD values for division. |AAD |No operands |ASCII Adjust before Division.
| | |if low nibble of AL > 9 or AF = 1 then: | | | |It works according to the following Algorithm: | | | |Corrects result in AH and AL after addition when |
|AAA |No operands |ASCII Adjust after Addition. This is especially important for Conditional Jump instructions (see "Program Flow Control" in Tutorials for more information). Some instructions generate exactly the same machine code, so disassemble may have a problem decoding to your original code. ? - flag value is undefined (maybe 1 or 0).
r - flag value depends on result of the instruction. These marks are used to show the state of the flags:Ġ - instruction sets this flag to 0. Include 'emu8086.inc' ORG 100h MOV AL, 1 MOV BL, 2 PRINTN 'Hello World!' macro. Here is an example that uses PRINTN macro:
Negate bx in emu8086 code#
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