Podcast
Questions and Answers
What will the 8086 do when it receives a low-to-high transition on its NMI input pin?
What will the 8086 do when it receives a low-to-high transition on its NMI input pin?
Why is the input pin on the 8086 called nonmaskable?
Why is the input pin on the 8086 called nonmaskable?
What does a pressure sensor on a large steam boiler connected to the NMI input do?
What does a pressure sensor on a large steam boiler connected to the NMI input do?
What is the main purpose of a type-3 interrupt in a system?
What is the main purpose of a type-3 interrupt in a system?
Signup and view all the answers
In a type 2 interrupt response, what is pushed onto the stack after the flags?
In a type 2 interrupt response, what is pushed onto the stack after the flags?
Signup and view all the answers
What happens after a break point is inserted into a system?
What happens after a break point is inserted into a system?
Signup and view all the answers
Why is it important that the NMI input pin's type 2 interrupt response cannot be masked?
Why is it important that the NMI input pin's type 2 interrupt response cannot be masked?
Signup and view all the answers
'Nonmaskable' for an input pin means that:
'Nonmaskable' for an input pin means that:
Signup and view all the answers
'Breakpoint' interrupts are primarily used for:
'Breakpoint' interrupts are primarily used for:
Signup and view all the answers
'Nonmaskable Interrupt' INT 2 in 8086 triggers when:
'Nonmaskable Interrupt' INT 2 in 8086 triggers when:
Signup and view all the answers
Study Notes
Interrupts and Interrupt Responses
- Interrupts break the normal sequence of execution of instructions, diverting the CPU to an Interrupt Service Routine (ISR) and then returning to the main program.
- There are three sources of interrupts:
- External signals applied to the Non-Maskable Interrupt (NMI) input pin or the Interrupt (INTR) input pin (hardware interrupts)
- Execution of the Interrupt instruction, INT (software interrupts)
- Error conditions produced by the execution of an instruction (e.g. divide by zero error)
Interrupt Procedure
- The interrupt procedure involves:
- Pushing flags and clearing IF and TF
- Pushing CS and IP on the stack
- Fetching the ISR address
- Executing the ISR procedure
- Popping IP, CS, and flags from the stack
- Returning to the main program using IRET
8259A Interrupt Operation
- To implement an interrupt, the interrupt enable flip-flop in the microprocessor should be enabled by writing the EI (8085) or STI (8086) instruction.
- The 8259A should be initialized by writing control words in the control register, including Initialization Command Words (ICWs) and Operational Command Words (OCWs).
- ICWs set up the proper conditions and specify vector address, while OCWs perform functions such as masking interrupts and setting up status-read operations.
Single 8259 Operation
- A single 8259 can accept 8 interrupts.
- When a device interrupts 8259, 8259 interrupts the microprocessor on the INTR pin.
- The sequence of events when an interrupt occurs includes:
- Setting the corresponding bit in the Interrupt Request Register (IRR)
- The Priority Resolver determining the highest priority interrupt
- Storing the ISR address in the Interrupt Vector Table (IVT)
Non-Maskable Interrupt (NMI)
- The 8086 automatically performs a type 2 interrupt response when it receives a low-to-high transition on its NMI input pin.
- The type 2 interrupt response cannot be disabled (masked) by any program instructions.
- NMI is used to signal the 8086 that some condition in an external system must be taken care of.
Breakpoint Interrupt (INT 3)
- The type 3 interrupt is used to implement a breakpoint function in a system.
- A breakpoint is used to examine the CPU and memory after the execution of a group of instructions.
- When a breakpoint is inserted, the system executes the instructions up to the breakpoint and then goes to the breakpoint procedure.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Test your knowledge on interrupts, including 8259 PIC and 8086 interrupts. Understand the concept of interrupts, how they break the sequence of operations, divert execution to Interrupt Service Routines (ISRs), and then transfer control back to the main program.
