The Program Counter (PC)

The Program Counter (PC) is a 2-byte address which tells the 8051 where the next instruction to execute is found in memory. When the 8051 is initialized PC always starts at 0000h and is incremented each time an instruction is executed. It is important to note that PC isn't always incremented by one. Since some instructions require 2 or 3 bytes the PC will be incremented by 2 or 3 in these cases. The Program Counter is special in that there is no way to directly modify its value. That is to say, it is not possible to do something like PC=2430h. On the other hand, if there is to execute LJMP 2430h there is need to effectively accomplished the same thing.
                                                                  Another important register in the 8051 is the PC (program counter). The program counter points to the address of the next instruction to be executed. As the CPU fetches the opcode from the program ROM, the program counter is incremented to point to the next instruction. The program counter in the 8051 is 16 bits wide. This means that the 8051 can access program addresses 0000 to FFFFH, a total of 64K bytes of code.






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