11

µPD75P218

3.2

16K-BYTE MODE AND 32K-BYTE MODE SWITCHING

16K-byte mode and 32K-byte mode are switched by the stack bank selection register. The stack bank selection

register format is shown in Fig. 3-1.

The stack bank selection register is set by 4-bit memory manipulation instruction. RESET input sets bit 3 of the

stack bank selection register to “1” and changes from 32K-byte mode to 16K-byte mode. When 16K-byte mode is

used, manipulating the stack bank selection register is unnecessary. When 32K-byte mode is used, the stack bank

selection register must always be initialized to 00

××B Note 1 at the beginning of the program.

Fig. 3-1 Stack Bank Selection Register Format

Stack area specification

0

0

Memory bank 0

0

1

Memory bank 1

1

0

Memory bank 2

1

1

Memory bank 3

0

Be sure to write 0 to bit 2.

0

32K-byte mode

1

16K-byte mode Note 2

Mode change specification

SBS0

SBS1

SBS2

SBS3

0

1

2

3

SBS

Symbol

F84H

Address

Caution When using 32K-byte mode, execute a subroutine call instruction and an interrupt enable instruc-

tion after the stack bank selection register is set after RESET input.

Notes 1. Set the desired value in

××.

2. When the 16K-byte mode is used after RESET input, the stack bank selection register does not have

to be manipulated.