Overview
The 8086 microprocessor has a built-in interrupt mechanism that allows the microprocessor to respond to external events, such as hardware interrupts, software interrupts, and exceptions. When an interrupt occurs, the microprocessor stops executing the current program and jumps to a specific location in memory, called the interrupt vector, to execute an interrupt service routine (ISR) that handles the interrupt.
The 8086 microprocessor supports two types of interrupts: hardware interrupts and software interrupts. Hardware interrupts are generated by external devices, such as the keyboard, mouse, or disk drive, to request the microprocessor’s attention. Software interrupts are generated by the program being executed to request a specific system service, such as input/output operations or memory allocation.
The 8086 microprocessor has 256 interrupt vectors, each of which corresponds to a specific interrupt number. The interrupt vector table is a section of memory that contains the addresses of the ISR for each interrupt number. The interrupt vector table is located in the first 1 KB of memory, starting at address 0x0000.
When an interrupt occurs, the microprocessor pushes the current values of the flags, CS (Code Segment) register, and IP (Instruction Pointer) register onto the stack, and sets the flags register to indicate that interrupts are enabled. The microprocessor then reads the address of the ISR from the interrupt vector table and jumps to that location to execute the ISR. Once the ISR has completed its task, it returns control to the main program by popping the values of the flags, CS, and IP registers from the stack.
The 8086 microprocessor also supports nested interrupts, which allow multiple interrupts to occur simultaneously. When a higher-priority interrupt occurs while the microprocessor is executing a lower-priority interrupt service routine, the microprocessor saves the current interrupt context on the stack and jumps to the ISR for the higher-priority interrupt. Once the higher-priority ISR has completed its task, the microprocessor restores the context of the lower-priority ISR and continues executing the lower-priority ISR.
In summary, the 8086 microprocessor has a built-in interrupt mechanism that allows the microprocessor to respond to external events. When an interrupt occurs, the microprocessor stops executing the current program and jumps to a specific location in memory to execute an ISR. The 8086 microprocessor supports hardware interrupts and software interrupts, and has a 256-entry interrupt vector table to store the addresses of the ISRs. The microprocessor also supports nested interrupts, which allow multiple interrupts to occur simultaneously.
Types of 8086 microprocessor interrupts
The 8086 microprocessor supports two types of interrupts: hardware interrupts and software interrupts. Both types of interrupts are used to request the microprocessor’s attention and trigger the execution of an interrupt service routine (ISR). Here is a detailed explanation of the two types of interrupts:
- Hardware Interrupts: Hardware interrupts are generated by external devices to request the microprocessor’s attention. These interrupts can be generated by a wide range of hardware devices, such as the keyboard, mouse, disk drive, or timer. The hardware interrupts are assigned specific interrupt numbers, ranging from 0 to 255. The interrupt numbers and the corresponding interrupt service routine (ISR) addresses are stored in the interrupt vector table, which is located in the first 1 KB of memory. When a hardware interrupt occurs, the microprocessor stops executing the current program, saves the current program state, and jumps to the ISR address specified by the interrupt vector table.
There are three types of hardware interrupts in the 8086 microprocessor:
a) Maskable Interrupts: These are interrupts that can be disabled or enabled by the programmer using the interrupt enable flag (IF) in the flags register. If the IF flag is set, the microprocessor responds to maskable interrupts. If the IF flag is cleared, the microprocessor ignores maskable interrupts. Examples of maskable interrupts include the keyboard, serial port, and parallel port interrupts.
b) Non-maskable Interrupts: These are interrupts that cannot be disabled by the programmer. These interrupts have the highest priority and are used for critical system tasks, such as system reset and hardware malfunction. Examples of non-maskable interrupts include power failure, clock failure, and parity error.
c) Software Interrupts: These are interrupts that are generated by the program being executed to request a specific system service. Software interrupts are also called system calls or trap instructions. The software interrupts are assigned specific interrupt numbers, ranging from 0 to 255, and the corresponding ISR addresses are stored in the interrupt vector table.
- Software Interrupts: Software interrupts are generated by the program being executed to request a specific system service, such as input/output operations or memory allocation. The software interrupts are generated using the INT instruction, which takes an interrupt number as its operand. The software interrupts are also called system calls or trap instructions. The software interrupts are assigned specific interrupt numbers, ranging from 0 to 255, and the corresponding ISR addresses are stored in the interrupt vector table.
The software interrupts are used for various system tasks, such as disk operations, memory management, and process synchronization. The software interrupts are also used for interfacing with the operating system and system utilities.
In summary, the 8086 microprocessor supports two types of interrupts: hardware interrupts and software interrupts. Hardware interrupts are generated by external devices and are assigned specific interrupt numbers. The interrupt numbers and corresponding ISR addresses are stored in the interrupt vector table. Software interrupts are generated by the program being executed using the INT instruction and are also assigned specific interrupt numbers. The software interrupts are used for various system tasks, such as disk operations, memory management, and process synchronization.
