UPD17147 datasheet(19/102 Pages) NEC

19 / 102 page

µPD17145(A1), 17147(A1), 17149(A1)

4. STACK

The stack is a register to which the return address of the program or the contents of the system registers,

which are described later, are saved when a subroutine call instruction is executed or when an interrupt is

acknowledged.

4.1 Configuration of Stack

Figure 4-1 shows the configuration of the stack.

The stack consists of a 3-bit binary counter, stack pointer (SP), five 10-bit (

µPD17145(A1)), 11-bit

(

µPD17147(A1)), or 12-bit (µPD17149(A1)) address stack registers (ASRs), and three 5-bit interrupt stack

registers (INTSKs).

Figure 4-1. Configuration of Stack

4.2 Stack Function

The stack is used to save a return address when the subroutine call or table reference instruction is executed.

When an interrupt is acknowledged, the return address of the program and the contents of the program status

word (PSWORD) are automatically saved to the stack. After they are saved to the stack, all the bits of PSWORD

are cleared to 0.

SPb2

SPb1

SPb0

b11

b10

BCDSK0

BCDSK1

BCDSK2

CMPSK0

CMPSK1

CMPSK2

CYSK0

CYSK1

CYSK2

ZSK0

ZSK1

ZSK2

IXESK0

IXESK1

IXESK2

Stack pointer

(SP)

SP is initialized to 5H at

reset.

Address stack registers

(ASRs)

Address stack register 0

Address stack register 1

Address stack register 2

Address stack register 3

Address stack register 4

Interrupt stack registers

(INTSKs)

UPD17147 Datasheet(PDF) 19 Page - NEC

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