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Questions and Answers
What is an interrupt in the context of a microcontroller?
What is an interrupt in the context of a microcontroller?
What is the purpose of the interrupt service routine (ISR)?
What is the purpose of the interrupt service routine (ISR)?
What happens when a microcontroller receives an interrupt signal?
What happens when a microcontroller receives an interrupt signal?
What is the main difference between interrupt and polling?
What is the main difference between interrupt and polling?
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What is the benefit of using interrupts in a microcontroller?
What is the benefit of using interrupts in a microcontroller?
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What is the role of the microcontroller in polling?
What is the role of the microcontroller in polling?
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What is the first step in executing an interrupt?
What is the first step in executing an interrupt?
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What is the purpose of the interrupt vector table?
What is the purpose of the interrupt vector table?
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What is the last instruction of the interrupt service subroutine?
What is the last instruction of the interrupt service subroutine?
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What is the function of the IE register?
What is the function of the IE register?
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What is the purpose of the IP register?
What is the purpose of the IP register?
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How many sources of interrupts are there in the original 8051?
How many sources of interrupts are there in the original 8051?
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Study Notes
Interrupts
- An interrupt is an external or internal event that informs the microcontroller that a device needs its service.
Interrupt vs Polling
- Interrupts:
- The device notifies the microcontroller by sending an interrupt signal when it needs service.
- The microcontroller interrupts its current task and serves the device.
- The associated program is called the Interrupt Service Routine (ISR) or interrupt handler.
- Polling:
- The microcontroller continuously monitors the status of a given device.
- When conditions are met, it performs the service and moves on to monitor the next device.
Steps in Executing an Interrupt
- Finishes the current instruction and saves the address of the next instruction (PC) on the stack.
- Saves the current status of all interrupts internally (not on the stack).
- Jumps to a fixed location in memory, the interrupt vector table, which holds the address of the ISR.
- Retrieves the address of the ISR from the interrupt vector table and jumps to it.
- Executes the interrupt service subroutine until the RETI (return from interrupt) instruction.
- Upon executing RETI, the microcontroller returns to the interrupted location.
8051 Interrupts
- The original 8051 has 6 sources of interrupts: Reset (RST), Timer 0 overflow (TF0), Timer 1 overflow (TF1), External Interrupt 0 (INT0), External Interrupt 1 (INT1), and Serial Port events (RI+TI).
- 8051 Interrupt Vectors: 8
- 8051 Interrupt-related Registers: 9
Interrupt-related Registers
- TCON: Edge and Type bits for External Interrupts 0/1
- SCON: RI and TI interrupt flags for RS232 (Serial Communication)
- IE: Interrupt Enable (responsible for enabling/disabling interrupts)
- IP: Interrupt Priority (assigns high or low priority to interrupts)
Enabling and Disabling Interrupts
- The IE (Interrupt Enable) register enables (unmasks) or disables (masks) interrupts.
- IE Register:
- EA: Global enable/disable
- ES: Enable Serial port interrupt
- ET1: Enable Timer 1 control bit
- EX1: Enable External 1 interrupt
- ET0: Enable Timer 0 control bit
- EX0: Enable External 0 interrupt
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Description
Learn about interrupts in microcontrollers, how they work, and their difference from polling. Understand the concept of interrupt service routine and how microcontrollers serve multiple devices.
