DIAGRAM OF VECTORED INTERRUPTS
The diagram of vector interrupts is shown in figure.
EXPLANATION OF DIAGRAM
When the user program is executed and suppose an interrupt occur then the CPU have
to execute a service routine to provide service to the interrupt. So when the ISR execute
it return back to the CPU for the next instruction.
So, the way the processor(CPU) chooses the branch address of interrupt service
Routine (ISR) varies from one unit to another.
There are to methods,
 Vector interrupt
 Non-vector interrupt
VECTORED INTERRUPTS
• A vectored interrupt is where the CPU knows
the address of the Interrupt Service Routine in
advance.
• In a computer, a vectored interrupt is an I/O
interrupt that tells the part of the computer
that handles I/O interrupts at the hardware
level that a request for attention from an I/O
device has been received and and also
identifies the device that sent the request.For
example: RST7. 5, RST6. ..
NON VECTORED INTERRUPTS
• Non-Vectored Interrupts are those
in which vector address is not
predefined. The interrupting device
gives the address of sub-routine for
these interrupts. For example,
INTR....
DIFFERENCE
Vector interrupt
• The ISR address of this interrupts is known to
CPU.
• The ISR address of this interrupts is fixed.
• The microprocessor jumps to the specific service
routine.
• When the microprocessor executes the call instruction,
it saves the address of the next instruction on the stack.
• At the end of the service routine, the RET instruction
returns the execution to where the program was
interrupted.
• All 8051 interrupts are vectored interrupts.
Non-vector interrupt
• Address of this common ISR is known to the
CPU.
• The interrupts which don’t have fixed memory
location for transfer of control from normal
execution.
• The address of the memory is sent along with the
interrupt..
• Once the interrupt occurs, the system must determine
which device, of all the devices associated actually
interrupted.
VECTOR
INTERRUPT
• A vectored interrupt is where the CPU
knows the address of the interrupt service
routine in advance. All it needs is that the
interrupting device sends its unique vector
through a data bus and through its I/O
interface to the CPU. The CPU takes this
vector, checks an interrupt table in memory
and then carries out the correct ISR for that
device. Therefore, the vectored interrupt
allows the CPU to be able to know that ISR to
carry out in software (memory)
NON VECTOR
INTERRUPT
• A non–vectored interrupt is where
the interrupting device never sends
an interrupt vector. An interrupt is
received by the CPU and it jumps the
program counter to a fixed address in
hardware.
• In an Interrupt Structure of 8086 system the first 1 Kbyte of memory from 00000H to
003FFH is reserved for storing the starting addresses of interrupt service routines.
• This block of memory is often called the Interrupt Vector Table in 8086 or
the interrupt pointer table.
• Since 4 bytes are required to store the CS and IP values for each interrupt service
procedure, the table can hold the starting add.
• When the 8086 responds to an interrupt, it automatically goes to the specified location
in the Interrupt Vector Table in 8086 to get the starting address of interrupt service
routine.
• So user has to load these starting addresses for different routines at the start of the
program.
TYPES
• Each interrupt type is given a number between 0 to 255 and the
address of each interrupt js found by multiplying the type by 4 e.g.
for type 11, interrupt address is 11 x 4 = 4410= 0002CH
• Only first five types have explicit definitions such as divide by zero
and non maskable interrupt.
• The next 27 interrupt types, from 5 to 31, are reserved by Intel for
use in future microprocessors.
• The upper 224 interrupt types, from 32 to 255, are available for user
for hardware or software interrupts.
•
DETERMINING ADDRESS
THROUGH INTERRUPT
VECTOR TABLE
All interrupts are assigned a number from 0 to
255, with each of these interrupts being
associated with a specific interrupt vector.
Interrupts 0, 1, 3, 4, 6 and 7 are generated by
the processor.
Interrupts from 8 to 15 and interrupt 2 are
generated by external hardware.
Most other interrupts are generated by
software.
• The first two bytes store the offset and the next two
store the segment address.
• To find the vector for an interrupt routines, we simply
multiply it by 4.
• INT n. Here, n is the type number.
CONT.
• Then we get memory location of Offset Address= n*4
• The segment address is in the next word.
• Memory location of Segment address= Memory
Location of Offset address+2
• With memory location obtained by this formulae, we
search for Offset : Segment addresses in IVT. Through
these we can find physical address of interrupt
routines.
Vector
diagram
Vector and
non-vectors
Difference
Vector
interrupt
table
Determine
the address
through table