Interrupt Priority of MCS-51 Series Microcontrollers

In the default state, the interrupt priority control register IP is 0, and all interrupt sources are at low priority. When all interrupt sources are at the same priority and request interrupts from the CPU at the same time, the CPU responds in order of priority; the conditions for interrupt nesting are: the interrupt source that the CPU responds to first should be at a low priority, and when the CPU executes the interrupt service program of the interrupt source, another interrupt source with a higher priority requests an interrupt. Interrupt sources with the same priority cannot achieve interrupt nesting. That is, interrupt nesting means being interrupted again during the interrupt service process! The so-called priority is strictly a queuing mechanism, and there is no nesting between them.

1. If multiple interrupts occur at the same time, the interrupt with higher priority will be  
executed first. 2. If multiple interrupts occur at the same time  
, the interrupt with higher priority will be executed first. 3. When a low-priority interrupt is being executed, a high-priority interrupt can interrupt the low-priority interrupt program 
. 4. When a low-priority interrupt is being executed, a high-priority interrupt with higher priority cannot interrupt the low-priority interrupt program.

This question is like when you go to the hospital to see a doctor, there are general registration, emergency number, and special rescue number (such as Comrade Xiao Hu was assassinated).

Now there is only one doctor in the hospital. Normally, the doctor diagnoses the patients with ordinary registration in sequence. When there is an emergency patient, the doctor stops diagnosing the ordinary patients and goes to diagnose the emergency patient. When the emergency patient is operating, a special rescue patient comes. The doctor immediately stops rescuing the emergency patient and rushes to rescue the special rescue patient. After rescuing the special rescue patient, the doctor returns to the emergency patient's operating room and continues to operate on him. After completing the emergency patient's operation, the doctor returns to his office to diagnose the ordinary patients.

The level of registration is different, and the doctor's treatment is also different. In the end, there are too few doctors in the hospital. One doctor can only see one patient at a time. The single-core era is like this hospital. There is only one person who can do things, and all things have to wait in line.