CHAPTER 3 REGISTERS

3.2Program Counter (PC) and Stack Pointer (SP)

The program counter (PC) and stack pointer (SP) are application-specific registers existing in the CPU.

The program counter (PC) indicates the address of the location at which the instruction currently being executed is stored.

The stack pointer (SP) holds the addresses of the data location to be referenced by the interrupt and stack push/pop instructions. The value of the current stack pointer (SP) indicates the address at which the last data pushed onto the stack is stored.

Program Counter (PC)

Figure 3.2-1shows the operation of the program counter (PC).

Figure 3.2-1 Program Counter Operation

Before execution

PC 1234H

MEMORY

 

 

After execution

 

MEMORY

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PC

1235H

 

 

1235H

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

XXH

 

 

 

 

 

 

 

 

 

 

 

1234H

00H

 

Instruction "NOP" executed

 

1234H

00H

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Stack Pointer (SP)

Figure 3.2-2shows the operation of the stack pointer (SP).

Figure 3.2-2 Stack Pointer Operation

Before execution

 

MEMORY

 

 

After execution

A

 

 

 

5679H

 

 

 

 

 

 

 

1234H

 

 

XXH

 

 

 

A

1234H

 

 

 

 

 

 

 

 

 

 

 

5678H

 

 

 

 

 

 

 

 

 

 

 

XXH

 

 

 

 

 

 

SP

5678H

 

 

 

 

 

SP

5676H

 

 

 

5677H

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5676H

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PUSHW A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MEMORY

 

 

 

5679H

XXH

 

 

 

5678H

XXH

 

 

 

5677H

32H

 

 

 

 

5676H

12H

 

 

 

 

 

 

 

17

Page 29
Image 29
Fujitsu F2MC-8FX manual Program Counter PC and Stack Pointer SP