Each Double Word interrupt vector is identified by a number from 0 to 255 INTEL

Each double word interrupt vector is identified by a

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Each Double Word interrupt vector is identified by a number from 0 to 255 INTEL calls this number the TYPE of the interrupt CSE – 341 : Microprocessors BRAC University
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Interrupt Types based on ISR ID 15 AVAILABLE 3FFH TYPE 255 FOR USER ... (224) 080H TYPE 32 TYPE 31 RESERVED (27) ... 014H TYPE 5 TYPE 4 010H INTO OVERFLOW TYPE 3 Predefined/ 00CH INT Dedicated/Internal TYPE 2 Interrupts Pointers 008H NON-MASKABLE (5) TYPE 1 004H SINGLE STEP CS Base Address TYPE 0 IP Offset 000H DIVIDE ERROR CSE – 341 : Microprocessors BRAC University
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Divide by zero interrupt- Type 0 16 It occurs automatically when the result of DIV or IDIV is too large Example: DIV BL //This will do AX÷BL //will put result in AL(quotient) and AH(reminder) If AX was 4000H and BL was 02H, The quotient is 2000H and reminder is 00H. µP can put 00H in AH(reminder) But it cannot put 2000H in AL(quotient) This condition is called divide error! CSE – 341 : Microprocessors BRAC University
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Single Step Interrupt- Type 1 17 In single step mode, a system will stop after it executes each instructions and wait for further direction If the 8086 trap flag is set, the 8086 will automatically do a type 1 interrupt after each instruction executes The trap flag is reset when the 8086 does a type 1 interrupt, so the single step mode will be disabled during the interrupt-service procedure Tasks for implementing single stepping: Set the trap flag Write an interrupt service procedure which saves all registers on the stack The stack where they can later be examined Load the starting address of the type 1 interrupt service procedure into address 00004H and 00006H CSE – 341 : Microprocessors BRAC University
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Non-maskable Interrupt- Type 2 18 The 8086 will automatically do a type 2 interrupt response when it receives a low to high transition on its NMI input pin The 8086 gets the CS value for the start of the type 2 interrupt service procedure from address 0000AH and the IP value for the start of the procedure from address 00008H The type 2 interrupt response cannot be disabled by any program instruction that’s why we use it to signal the 8086 that some condition in an external system must be taken care of The type 2 interrupt is useful to save program data in case of a system power failure CSE – 341 : Microprocessors BRAC University
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Breakpoint Interrupt- Type 3 19 The main use of type 3 interrupt is to implement a breakpoint function in a system Unlike the single step feature, which stops execution after each instruction, the breakpoint feature executes all the instruction up to the inserted breakpoint and then stops execution The 8086 gets the CS value for the start of the type 3 interrupt service procedure from address 0000EH and the IP value for the start of the procedure from address 0000CH It is useful in debugging large programs when single stepping is inefficient CSE – 341 : Microprocessors BRAC University
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Overflow Interrupt- Type 4 20 The 8086 overflow flag (OF) will be set if the signed result of an arithmetic
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  • Spring '17
  • Dr. Jia uddin
  • Interrupt, BRAC University

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