NEC PD17062 Manuale Utente

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The stack is a register used to save an address returned by a program or the contents of the system register,

described later, when a subroutine call occurs or an interrupt is accepted.

The stack consists of a stack pointer (SP), which is a 4-bit binary counter, six 13-bit address stack registers

(ASRs), and two 3-bit interrupt stack registers.

The stack pointer is located at address 01H in the register file, and specifies an address stack register.  The

contents of the stack pointer are decremented by 1 whenever a push operation (CALL, MOVT, or PUSH

instruction or interrupt acceptance) is performed, or incremented by 1 whenever a pop operation (RET, RETSK,

RETI, MOVT, or POP instruction) is performed.

The high-order bit of the stack pointer is always set to 0.  The stack pointer can indicate any of eight different

values, 0H to 7H.  However, 6H and 7H are not assigned to the stack.

0

(SPb

2

)

(SPb

1

)

(SPb

0

)

MSB

LSB

         Instruction

Stack pointer value

CALL addr

CALL @AR

MOVT DBF, @AR

SP – 1

PUSH AR

Interrupt acceptance

RET

RETSK

MOVT DBF, @AR

SP + 1

POP AR

RETI