UPD75P4308GS datasheet(13/60 Pages) NEC

13 / 60 page

µPD75P4308

4.2 Setting of Stack Bank Selection (SBS) Register

Use the stack bank selection register to switch between the Mk I mode and the Mk II mode. Figure 4-1 shows the

format for doing this.

The stack bank selection register is set using a 4-bit memory manipulation instruction. When using the Mk I mode,

be sure to initialize the stack bank selection register to 1000B at the beginning of the program. When using the Mk

II mode, be sure to initialize it to 0000B.

Figure 4-1. Format of Stack Bank Selection Register

SBS3

SBS2

SBS1

SBS0

F84H

Address

SBS

Symbol

Stack area specification

Memory bank 0

Be sure to enter “0” for bit 2.

Mk II mode

Mk I mode

Mode selection specification

Setting prohibited other than above

Cautions 1. SBS3 is set to “1” after RESET input, and consequently the CPU operates in the Mk I mode.

When using instructions for the Mk II mode, set SBS3 to “0” to enter the Mk II mode before

using the instructions.

2. When using the Mk II mode, execute a subroutine call instruction and an interrupt instruction

after RESET input and after setting the stack bank selection register.

UPD75P4308GS Datasheet(PDF) 13 Page - NEC