What is CLD Assembly?
Description. The cld instruction clears the direction flag: DF = 0. The direction flag (DF) is used to influence the direction in which some of the instructions work when used with the REP* prefix. There is a number of instructions that are influenced by this flag directly, for example MOVS, LODS, SCAS.
What is difference between STD and CLD?
CLD CLears the Direction flag, data goes onwards. STD SeTs the Direction flag, data goes backwards. Under STDCALL, the direction flag is clear on entry and must be returned clear.
What happens when CLD is executed 8086?
CLD Instruction : This instruction is used to reset the direction flag to zero, so that SI and/or DI can be incremented automatically after execution of string instructions. CLD does not affect any other flag.
What is STD in assembly?
Set Direction Flag (std)
What is Stosb?
The explicit-operands form (specified with the STOS mnemonic) allows the destination operand to be specified explicitly. The size of the destination and source operands is selected with the mnemonic: STOSB (byte read from register AL), STOSW (word from AX), or STOSD (doubleword from EAX).
What is Lodsb Assembly?
The explicit-operands form (specified with the LODS mnemonic) allows the source operand to be specified explicitly. The size of the source and destination operands is selected with the mnemonic: LODSB (byte loaded into register AL), LODSW (word loaded into AX), or LODSD (doubleword loaded into EAX).
What is SI register?
SI – This is the source index register. It is of 16 bits. It is used in the pointer addressing of data and as a source in some string related operations. It is used in the pointer addressing of data and as a destination in some string related operations.
How do you use Lodsd?
The LODSD instruction The LODSD loads the double word addressed by DS:[SI] into register EAX. SI is then incremented (if DF=0) or decremented (if DF=1) by 4. Note that repeat prefixes cannot be used with load string instructions as their use does not make sense.
How does CMP work in 8086?
The CMP instruction compares two operands. This instruction basically subtracts one operand from the other for comparing whether the operands are equal or not. It does not disturb the destination or source operands. It is used along with the conditional jump instruction for decision making.
What are the different types of instructions in 8086 microprocessor?
Arithmetic Instructions
| Instruction | Description |
|---|---|
| SBB | Subtract immediate data with borrow from accumulator, memory or register. |
| MUL | Unsigned 8-bit or 16-bit multiplication. |
| IMUL | Signed 8-bit or 16-bit multiplication. |
| DIV | Unsigned 8-bit or 16-bit division. |
What do you mean by Xchg instruction for 8086?
The XCHG instruction exchanges the content of a register with the content of another register or with the content of memory location(s). It cannot directly exchange the content of two memory locations. The source and destination must both be of the same type (bytes or words).
What are directives in 8086?
Introduction: Assembler directives are the directions to the assembler which indicate how an operand or section of the program is to be processed. These are also called pseudo operations which are not executable by the microprocessor.