The LOOP instruction is mainly used to simulate the different loops in HLL. The Loop instructions use the CX register to indicate the loop count. Note that the ECX register can be used as a loop counter in 32-bit mode.

Which register is used in loop instructions?

The LOOP instruction assumes that the ECX register contains the loop count. When the loop instruction is executed, the ECX register is decremented and the control jumps to the target label, until the ECX register value, i.e., the counter reaches the value zero.

What does loop instruction do?

The loop instruction always extracts the number of iterations from the ECX register. The loop instruction decrements the value of ECX and compares it with zero. If the value in ECX is equal to zero, the program jumps to the L1 label; otherwise, the program exits the loop.

Which register is used as counter register for loop instructions?

CX is used as a default counter in case of string and loop instructions. The loop instruction is executed based on the value in the CX register.

Which register content is decrement by one in loop instructions?

Looping in the 8051

An instruction DJNZ reg, label is used to perform a Loop operation. In this instruction, a register is decremented by 1; if it is not zero, then 8051 jumps to the target address referred to by the label.

x86 Assembly Language - Using Registers, Variables, and the LOOP Instruction Together

39 related questions found

Which of the following flags gets affected when a compare instruction ie Cmpsb Cmpsw or Cmpsd is executed?

Which of the following flags gets affected when a compare instruction, i.e. CMPSB, CMPSW or CMPSD is executed? Explanation: Whenever a compare instruction over strings is executed, the status flags are affected. From the mentioned options, only Zero Flag is a status flag.

Which flag are affected by CMP instruction?

CMP and TEST instructions affect flags only and do not store a result (these instruction are used to make decisions during program execution). These instructions affect these flags only: CF, ZF, SF, OF, PF, AF.

Which register is used as a default counter in case of string and loop instructions?

CX register is used as a default counter in case of string and loop instructions. DX register is used as an implicit operand or destination in case of a few instructions.

Which group of instructions do not affect the flags Mcq?

As there is no arithmetic or logical operation being performed, no flags are affected by data transfer instructions. Arithmetic instruction: Arithmetic Instructions are the instructions that perform basic arithmetic operations such as addition, subtraction, and a few more.

Which registers are used in string instructions for data manipulation by default in 8086?

By default, the processor assumes that the DI register references the ES segment in string manipulation instructions. ES register can be changed directly using POP and LES instructions.

What are general data registers?

General purpose registers are used to store temporary data within the microprocessor. There are 8 general purpose registers in 8086 microprocessor. ... It is of 16 bits and is divided into two 8-bit registers AH and AL to also perform 8-bit instructions.

How many registers are there in 8086 microprocessor?

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). 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.

What does CMP do in assembly?

The CMP instruction compares two operands. It is generally used in conditional execution. This instruction basically subtracts one operand from the other for comparing whether the operands are equal or not.

What is index register function?

An index register in a computer's CPU is a processor register or assigned memory location used for modifying operand addresses during the run of a program. This proved useful for doing vector/array operations and in commercial data processing for navigating from field to field within records.

In which register CMP instruction stores its result?

This instruction is used to compare contents of the Accumulator with given register R. ... The result of compare operation will be stored in the Temp register. Temp is not a GPR (General Purpose Register) but an internal register that is not accessible to the programmer.

What is ECX register?

CX is known as the count register, as the ECX, CX registers store the loop count in iterative operations. DX is known as the data register. It is also used in input/output operations. It is also used with AX register along with DX for multiply and divide operations involving large values.

Which of the following instructions affect carry flag?

The logical instructions that affect the carry flag during its execution are RL, RLC, RRC and RR. Solution: The instruction, CPL Bit is used to complement or invert the bit of a bit addressable SFR or RAM.

Which of the following instruction affects carry flag Mcq?

While STC instruction executes, microprocessor sets the carry flag to 1. So this instruction affects the carry flag only.

Which type of instruction does not affect the 8085 flag?

CMA does not affect flags. If you need to evaluate a logical condition on the result of CMA, you should use CPI 0 after CMA.

Which register hold offset?

Stack pointer (SP) holds the offset address of the stack segment. 4. Base pointer (BP) can be used general register and also used to hold offset address in few instructions.

Which register is used as counter?

Explanation: The CX register is known as counter register it is an 16-bit register that are classified into the two 8-bit CH and CL registers also it executed 8-bit instructions in the 8086 microprocessor. The CX register is used in the 8086 Microprocessor for the looping and the rotation purpose . For example.

What is the purpose of CS register?

The CS(code segment register) is used to address the code segment of the memory i.e a location in the memory where the code is stored. The IP(Instruction pointer) contains the offset within the code segment of the memory.

Which flags can be affected by and operation?

In fact, as mentioned earlier, a particular instruction may affect a number flags simultaneously – or none at all. For example, both ADD and SUB affect the carry, overflow, sign, zero and parity flags. INC and Dec affect all of these except the carry flag, and Mov affects none of the flags at all.

What is Scasb instruction?

The SCAS instruction is used for searching a particular character or set of characters in a string. The data item to be searched should be in AL (for SCASB), AX (for SCASW) or EAX (for SCASD) registers. The string to be searched should be in memory and pointed by the ES:DI (or EDI) register.

Which instruction uses AF flag?

Auxiliary Carry Flag (AF) is one of the six status flags in the 8086 microprocessor. This flag is used in BCD (Binary-coded Decimal) operations. The status of this flag is updated for every arithmetic or logical operation performed by ALU.