MCU execution program process

The process of computer execution of program is actually to repeat the above operation process one by one until the stop instruction is encountered and the instruction can be looped and waited for. 

When a general computer is working, the program and data must first be sent to the memory through the input interface circuit and the data bus through the external device, and then taken out and executed one by one. However, the program in the single-chip microcomputer is generally solidified in the on-chip or off-chip program memory through the writer in advance. Therefore, the instruction can be executed as soon as the computer is turned on. 

Below we will give an example to illustrate the execution process of the instruction: 

when the computer is turned on, the program counter PC changes to 0000H. Then the single-chip microcomputer automatically enters the execution process of the program under the action of the timing circuit. The execution process is actually a cycle of taking out instructions (taking out the instructions stored in the memory in advance) and executing instructions (analyzing and executing instructions). 

For example, the execution instruction: MOV A, #0E0H, its machine code is "74H E0H", the function of this instruction is to send the operand E0H to the accumulator, 

74H is stored in the 0000H unit, and E0H is stored in the 0001H unit. When the microcontroller starts running, it first enters the instruction fetch stage, and the order is: 
1 The content of the program counter (0000H at this time) is sent to the address register; 

2 The content of the program counter is automatically increased by 1 (becomes 0001H); 

3 The content of the address register (0000H) is sent to the memory through the internal address bus, and the address decoding circuit in the memory selects the unit with address 0000H; 

4 The CPU makes the read control line valid