Internal Expansion Ram Size Switching Register; Format Of Internal Expansion Ram Size Switching Register (Ixs) - NEC 78K0 User Manual

28.2 Internal Expansion RAM Size Switching Register

This register is used to set the internal expansion RAM capacity via software.
This register is set by an 8-bit memory manipulation instruction.
RESET input sets IXS to 0CH.
Caution Be sure to set the value of the relevant mask ROM version at initialization.
Figure 28-2. Format of Internal Expansion RAM Size Switching Register (IXS)
Address: FFF4H After reset: 0CH
Symbol 7
IXS 0
IXRAM4
0
0
The IXS settings required to obtain the same memory map as mask ROM versions are shown in Table 28-3.
Table 28-3. Internal Expansion RAM Size Switching Register Settings
Caution When using a mask ROM version, be sure to set the value indicated in Table 28-3 to IXS.
CHAPTER 28
R/W
6 5
0 0 IXRAM4
IXRAM3 IXRAM2 IXRAM1
1 1
1 0
Other than above
Target Mask ROM Versions *
µ
PD780143
µ
PD780144
µ
PD780146
µ
PD780148
User's Manual U15947EJ2V0UD
µ
PD78F0148
4 3 2
IXRAM3 IXRAM2
IXRAM0 Internal expansion RAM capacity selection
0 0 0 bytes
1 0 1024 bytes
Setting prohibited
IXS Setting
0CH
0CH
0AH
0AH
1 0
IXRAM1 IXRAM0
497