51 MCU Study Notes (IV)_Interrupt System-EEWORLD

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Related concepts

Interrupt source: The event that caused the interrupt
Interrupt request: The interrupt source makes a request to the CPU for processing
Breakpoint: The pause point of the program when an interrupt occurs
Interrupt response: The process by which the CPU pauses the current program and responds to an interrupt request
Interrupt handler: A program that handles an interrupt source
Interrupt processing: CPU executes the relevant interrupt processing program
Interrupt return: the process of returning to the breakpoint

The difference between interrupts and subroutines

Calling is somewhat similar, but the two are different concepts.

The source is different. Interrupts are generated by external interrupt sources and are unpredictable and random, such as throwing exceptions. Subroutines are called by the main program.
The responses are different. The interrupt system needs to protect the breakpoints and context, while the subroutine only needs to save the breakpoints.
The functions are different. The interrupt program mainly handles CPU external asynchronous events, and the subroutine call serves the main program.

Interrupt Type

External interrupt source: generated by external hardware resources. Up and down edge trigger and high and low level trigger.
Timing interrupt source: timer/counter overflow trigger.
Serial port interrupt source: triggered by sending or receiving completion information during serial communication.

TCON interrupt flag

IE1: External interrupt 1 request flag.
IT1: External interrupt 1 trigger mode selection bit. When IT1=0, it is low level trigger mode; when IT1=1, it is falling edge trigger mode.
IE0: External interrupt 0 request flag.
IT0: External interrupt 0 trigger mode selection bit. When IT0=0, it is low level trigger mode; when IT0=1, it is falling edge trigger mode.

SCON interrupt flag

RI: After receiving the information on the serial interface, the hardware automatically sets RI=1 and the CPU responds to the interrupt. Note that it will not automatically clear RI=0 and needs to be set by software
TI: After the serial interface completes sending information, the hardware automatically sets TI=1 and the CPU responds to the interrupt. Note that it will not automatically clear TI=0 and needs to be set by software

General steps for interrupt initialization

1. Determine the working mode (i.e. assign a value to TMOD);
2. Preset the initial value of timing or counting (the initial value can be directly written into TH0, TL0 or TH1, TL1);
3. Enable the interrupt of the timer/counter as needed (directly assign a value to the IE bit);
4. Start the timer/counter (if it is specified to be started by software, TR0 or TR1 can be set to "1"; if it is specified to be started by the external interrupt pin level, a start level needs to be added to the external pin. When the start requirements are met, the timer starts counting or timing according to the specified working mode and initial value).

Interrupt enable flag

EX1: External interrupt 1 enable bit;
EX0: external interrupt 0 enable bit;
ET1: Timer/Counter T1 interrupt enable bit;
ET0: Timer/Counter T0 interrupt enable bit;
ES: serial port interrupt enable bit;
EA: CPU interrupt enable (always enable) bit.

Interrupt priority flags

0 is low priority, 1 is high priority

PS: Serial interface interrupt priority setting bit
PT1: Timer/Counter Interrupt 1 Interrupt Priority Setting Bit
PT0: Timer/Counter Interrupt 0 Interrupt Priority Setting Bit
PX1: External interrupt 1 interrupt priority setting bit
PX0: External interrupt 0 interrupt priority setting bit

51 MCU interrupt number

External interrupt 0 (INT0), the corresponding interrupt number is 0, the interrupt entry address is 0003H
Timer/Counter 0 (T1), corresponding to interrupt number 1, interrupt entry address 000BH
External interrupt 1 (INT1), interrupt number 2 entry address 0013H
Timer/Counter 1 (T1) Interrupt Number 3 Entry Address 001BH
Serial port (RI/TI) interrupt number 4 Entry address 0023H
These five are AT89S51, 52 also has the following
Timer/Counter 2 (T2) interrupt number 5, entry address 002BH

Function name()interrupt 0 {} //Corresponding to external interrupt 0;
Function name ()interrupt 1 {} //Corresponding to timer/counter 0 interrupt;
Function name()interrupt 2 {} //Corresponding to external interrupt 1;
Function name ()interrupt 3 {} //Corresponding to timer/counter 1 interrupt;
Function name ()interrupt 4 {} //Corresponding to serial port interrupt;

There are 5 types of interrupts, with priority from top to bottom; [Quoted from Baidu Knows link]

Reference address：51 MCU Study Notes (IV)_Interrupt System

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