MOV Instruction
Used to Data transfer between memory cells, registers and the accumulator. Syntax is as follows:
MOV Destination, Source
The different movements of data allowed for this Instruction are shown in the table given next:
S. No. |
Destination |
Source |
1. |
memory |
accumulator |
2. |
accumulator |
memory |
3. |
segment register |
memory/register |
4 |
memory/register |
segment register |
5. |
Register |
register |
6. |
Register |
memory |
7. |
memory |
register |
8. |
Register |
immediate data |
9. |
memory |
immediate data |
Let us see an example:
MOV AX,0006
MOV BX,AX
MOV AX,4C00
INT 21
This program moves the value of 0006H to the AX register, then it moves the content of AX (0006h) to the BX register, and lastly it moves the 4C00h value to the AX register to end the execution with the 4C option of the 21h interruption. We’ll take a brief introduction of interrupt 13H and interrupt 21H later.
Interruptions
An interrupt is a hardware facility that causes the CPU to suspend execution, save its status, and transfer to a specific location. The transfer location specifies the address of a program that is intended to take action in response to the interrupt. The program that is executed as a result of the interrupt is called an interrupt- handling program.
For example, if DOS wants to send some information to the BIOS or BIOS wants to send some information to the computer system, DOS or BIOS generate interrupts. Whenever an interrupt is generated, computer suspends whatever it is doing and first takes care of the operation which has generated the interrupt.
Each device capable of generating interrupt is given a unique interrupt number to identify which device is generating these interrupts. We shall discuss all the functions and sub functions of interrupt 13H, Extensions of interrupt 13H and interrupt 21H within this book.
Basically, the interruptions may be of following three types:
- Internal hardware interruptions
- External hardware interruptions
- Software interruptions
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