NEC PD78078 用户手册
571
CHAPTER 27
µ
PD78P078, 78P078Y
7
0
Symbol
IXS
6
0
5
0
4
0
3
IXRAM3
2
IXRAM2
1
IXRAM1
0
IXRAM0
Address
FFF4H
0AH
After
Reset
Internal Extension RAM Capacity Selection
IXRAM3 IXRAM2 IXRAM1
1024 bytes
1
0
1
Setting prohibited
Other than above
IXRAM0
0
R/W
W
0 bytes
1
1
0
0
27.2 Internal Extension RAM Size Switching Register
The
µ
PD78P078 and 78P078Y allow users to define its internal extension RAM size by using the internal
extension RAM size switching register (IXS), so that the same memory mapping as that of a mask ROM version
with a different internal extension RAM is possible.
The IXS is set by an 8-bit memory manipulation instruction.
RESET signal input sets IXS to 0AH.
Caution When the
µ
PD78076, 78078, 78076Y, or 78078Y is used, be sure to set the value specified in
Table 27-3 to IXS. Other settings are prohibited.
Figure 27-2. Internal Extension RAM Size Switching Register Format
The value which is set in the IXS that has the identical memory map to the mask ROM versions is given in
Table 27-3.
Table 27-3. Examples of Internal Extension RAM Size Switching Register Settings
Relevant Mask ROM Version
IXS Setting
µ
PD78076, 78076Y
0AH
µ
PD78078, 78078Y