What is meant by assembler directives?

Assembler directives are directions to the assembler to take some action or change a setting. Assembler directives do not represent instructions, and are not translated into machine code. … data directive tells the assembler that information that follows is program data. The information following a .

What is .model flat in assembly?

Description: .386 It is the assembler directive, which tells to use the 80386 instruction set. There are many predecesor of this like 80486, 80586,etc .model flat, stdcall It tells which memory model to use.

What are the different types of assembler directives?

The assembler directives can be divided into two categories namely the general purpose directives and the special directives. . CODE- This assembler directive indicates the beginning of the code segment.

What are assembler directives in 8086?

An assembler directive is a statement to give direction to the assembler to perform task of the assembly process. It control the organization if the program and provide necessary information to the assembler to understand the assembly language programs to generate necessary machine codes.

What is the purpose of the .model tiny statement?

model small tells the assembler that you intend to use the small memory model – one code segment, one data segment and one stack segment – and the values of the segment registers are never changed.

What is .model large in assembly language?

MODEL LARGE): and Data can exceed 64K bytes. However no single data set (i.e. arra bytes (Code>64K and Data >64K). DEL HUGE): and Data can exceed 64K bytes.

Why assembler directives are called pseudo instructions?

Assembler directives are the instructions provided to the assembler, not the processor as the processor has nothing to do with these instructions. These instructions are also known as pseudo-instructions or pseudo-opcode.

What are assembler directives why it is essential in assembly language programming give examples?

An assembler directive is a message to the assembler that tells the assembler something it needs to know in order to carry out the assembly process; for example, an assemble directive tell the assembler where a program is to be located in memory.

What does mov ah 4CH mean?

MOV AH, 4CH means store (or “move”) the hexadecimal value 4C into register AH .

What is a macro in assembly language?

• An assembly language macro is a template whose format. represents a pattern of 0 or more assembly language statements that might be common to multiple programs. • For this purpose, a macro language is used to provide a syntax for. defining macros.

What is DB in assembly language?

DB = define byte size variables. DW = define word size (16 bits) variables. DD = define double word size (32 bits) variables.

Why is the DOS function 4Ch used?

Use function 4Ch instead. Description: This function will read a single character from the standard input device. If no character is waiting to be read, it will wait until a character becomes available. Description: This function will write the specified character on the standard output device.

What is the difference between MOV and Lea?

LEA stands for Load Effective Address. It takes the result from address generation, and puts that result directly in a register, without accessing memory. MOV , on the other hand, will move data to or from memory at the computed offset.

What is MOV in ALP?

The mov instruction copies the data item referred to by its second operand (i.e. register contents, memory contents, or a constant value) into the location referred to by its first operand (i.e. a register or memory).

What is 4Ch in assembly?

mov ah,4ch is the first line of assembler code. The value 4C in hexadecimal is stored in the register AH. int 21h is the second line of assembler code. The software interrupt 21h is called. This interrupt, when given the value of 4ch in AH (as is the case here), causes the program to exit immediately.

Which interrupt called DOS interrupt?

Interrupt vectors used by DOS
Interrupt vector Description Version
25h Absolute disk read 1.0+
26h Absolute disk write 1.0+
27h Terminate and stay resident 1.0+
28h Idle callout 2.0+

Is MS DOS a multitasking operating system?

DOS is not a multitasking operating system. DOS did however provide a Terminate and Stay Resident (TSR) function which allowed programs to remain resident in memory.

What is the function of 4Ch and int 21H?

INT 21h function 4Ch is preferred. Action: Reads a character from the standard input device and echoes it to the standard output device. If no character is ready it waits until one is available.

What is interrupt 21H?

INT 21H will generate the software interrupt 0x21 (33 in decimal), causing the function pointed to by the 34th vector in the interrupt table to be executed, which is typically an MS-DOS API call. … if there is no character in the keyboard buffer, the function waits until any key is pressed.

What is 2h in assembly language?

In 8086 assembly language, we do not call operating system subprograms by name, instead, we use a software interrupt mechanism • The 8086 INT instruction generates a software interrupt. … For example, the subprogram to display a character is subprogram number 2h. • This number must be stored in the ah register.

What is 21h in assembly language?

int 21h means, call the interrupt handler 0x21 which is the DOS Function dispatcher. the “mov ah,01h” is setting AH with 0x01, which is the Keyboard Input with Echo handler in the interrupt.