UPD17P133CS datasheet(53/289 Pages) NEC

53 / 289 page

CHAPTER 6

STACK

Table 6-2. Operation of the Stack Pointer during Execution

Instruction

Operation

CALL addr

<1> Stack pointer (SP) is decremented.

<2> Program counter (PC) is saved in the address stack register pointed to by the stack

pointer (SP).

<3> Value specified by the instruction operand (addr) is transferred to the program

counter.

RET

<1> Value in the address stack register pointed to by the stack pointer (SP) is restored

to the program counter (PC).

<2> Stack pointer (SP) is incremented.

When the RETSK instruction is executed, the first command after data restoration becomes a no operation

instruction (NOP).

6.6.2 Stack Operation during Table Reference (MOVT DBF, @AR)

Table 6-3 shows stack operation during table reference.

Table 6-3. Stack Operation during Table Reference

Instruction

Instruction Cycle

Operation

MOVT DBF, @AR

First

<1> Stack pointer (SP) is decremented.

<2> Program counter (PC) is saved in the address stack register

pointed to by the stack pointer (SP).

<3> Value in the address register (AR) is transferred to the program

counter (PC).

Second

<1> Contents of the program memory (ROM) pointed to by the pro-

gram counter (PC) is transferred to the data buffer (DBF).

<2> Value in the address stack register pointed to by the stack pointer

(SP) is restored to the program counter (PC).

<3> Stack pointer (SP) is incremented.

Remark

As an exception, execution of MOVT DBF and @AR instructions require two instruction cycle.

RETSK

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