The program counter (PC) is a register that manages the memory address of the instruction to be executed next.
The address specified by the PC will be + n (+1 for a 1-word instruction and +2 for a 2-word instruction) each time one instruction is executed.
However, in the case of an interrupt instruction, etc., the jump destination address is stored.
The CPU reads the address where the instruction to be executed next is stored from the PC and executes it in sequence.
For example, if 0x8020 (address) is stored in the PC, it means that the CPU is executing the instruction of the address 0x8019.
Then, if the address 0x8020 is read from the PC, the address 0x8021 for reading the instruction to be executed next by the CPU is stored in the PC.