UPD17072 datasheet(23/226 Pages) NEC

23 / 226 page

µPD17072,17073

ADDRESS STACK (ASK)

3.1 General

Figure 3-1 outlines the address stack.

The address stack consists of a stack pointer and an address stack register.

The address of the address stack register is specified by the stack pointer.

The address stack saves return addresses when a subroutine call instruction has been executed and when an

interrupt has been accepted.

The address stack is also used when a table reference instruction is executed.

Figure 3-1. Outline of Address Stack

3.2 Address Stack Register (ASR)

Figure 3-2 shows the configuration of the address stack register.

The address stack register consists of three 12-bit registers ASR0-ASR2. Actually, however, no register is

assigned to ASR2, and the address stack register therefore consists of two 12-bit registers (ASR0 and ASR1).

The address stack saves return addresses when a subroutine call instruction has been executed, when an interrupt

has been accepted, and when a table reference instruction is executed.

Figure 3-2. Configuration of Address Stack Register

Stack pointer

Address stack register

Return address

Specifies address

Address stack register (ASR)

Stack pointer

(SP)

Bit

Address

ASR0

ASR1

ASR2 (Undefined)

Cannot

be used

SP1 SP0

b11

b10

UPD17072 Datasheet(PDF) 23 Page - NEC