(1) How many bytes are used by the interrupt vector table?
(2) Interrupt vector table addresses 003F8H ~ 003FBH belong to
which interrupt?
(3) Please write an assembly code section to read the interrupt vector
of type 71H from the interrupt vector table to ES and BX.
(4) Suppose the address of IMR in an 8259A is 21H. What is the
purpose of the following program code?
IN AL,21H
AND AL,55H
OUT 21H,AL
Answers
Answer:
what is this what is it meaning
Answer :
1) 1024 bytes are used by the interrupt vector table
2) The last 224 interrupts come in the category of user interrupt vectors.
Therefore the correct answer to this question is User Interrupt.
4) The purpose of the following co_de is to perform AND operation .
IMR is the interrupt mark register we are going to store the values for doing AND operation in this and writing the co_de using 8259 microprocessor.
In line 1 the IN instruction is used to copy data from the port to accumulator. Here AL is the accumulator because the data is 8 bit .if 16 it should be AX. 21H is the address where the data is stored. The whole means copy a byte from the port 21H to AL.
AND operation should be in the format AND destination, source. Here the data in the accumulator and the in the port 55H will be multiplied. That is if all bits are high the output is high, if one bit is low the output should be low.
OUT is used to copy data from accumulator to an output port. Here the data in the address 21H will be replaced and stored in the accumulator. Copy contents of AL to 8 bit port 21H.
