Interrupts, Addressing Mode and Direct Memory Access
Interrupt
• An interrupt is a signal to the processor or an instruction in software usually indicating
an event that needs immediate attention.
• The processor responds by suspending its current activities, saving its state, and
executing a small program called an interrupt handler(interrupt service routine, ISR) to
deal with the event.
Types of interrupt:
• A hardware interrupt is an electronic alerting signal to the processor from an external
device, either a part of the computer itself such as a disk controller or an
external peripheral.
• A software interrupt is caused either by an exceptional condition in the processor itself,
or a special instruction in the instruction set which causes an interrupt when it is
executed.
Addressing Mode
• Addressing modes are an aspect of the instruction set architecture in most central
processing unit (CPU) designs.
• An addressing mode specifies how to calculate the effective memory address of an
operand by using information held in registers and/or constants contained within a
machine instruction or elsewhere.
Types of Addressing Modes
• Immediate Addressing
• Direct Addressing
• Indirect Addressing
• Register Addressing
• Register Indirect Addressing
• Relative Addressing
• Indexed Addressing
, Immediate Addressing: Here, the operand is given in the instruction itself. This mode is
used to define a constant or set initial values of variables. The advantage of this mode is
that no memory reference other than instruction fetch is required to obtain operand.
Direct Addressing: It requires one memory reference to read the operand from the given
location and provides only a limited address space.
Indirect Addressing: The address field of the instruction refers to the address of a word
in memory, which in turn contains the full length address of the operand.
Interrupt
• An interrupt is a signal to the processor or an instruction in software usually indicating
an event that needs immediate attention.
• The processor responds by suspending its current activities, saving its state, and
executing a small program called an interrupt handler(interrupt service routine, ISR) to
deal with the event.
Types of interrupt:
• A hardware interrupt is an electronic alerting signal to the processor from an external
device, either a part of the computer itself such as a disk controller or an
external peripheral.
• A software interrupt is caused either by an exceptional condition in the processor itself,
or a special instruction in the instruction set which causes an interrupt when it is
executed.
Addressing Mode
• Addressing modes are an aspect of the instruction set architecture in most central
processing unit (CPU) designs.
• An addressing mode specifies how to calculate the effective memory address of an
operand by using information held in registers and/or constants contained within a
machine instruction or elsewhere.
Types of Addressing Modes
• Immediate Addressing
• Direct Addressing
• Indirect Addressing
• Register Addressing
• Register Indirect Addressing
• Relative Addressing
• Indexed Addressing
, Immediate Addressing: Here, the operand is given in the instruction itself. This mode is
used to define a constant or set initial values of variables. The advantage of this mode is
that no memory reference other than instruction fetch is required to obtain operand.
Direct Addressing: It requires one memory reference to read the operand from the given
location and provides only a limited address space.
Indirect Addressing: The address field of the instruction refers to the address of a word
in memory, which in turn contains the full length address of the operand.
