Internal Expansion Ram Size Switching Register - NEC mPD780208 Subseries User Manual

19.2

Internal Expansion RAM Size Switching Register

By setting the internal expansion RAM size swtiching register (IXS), the µ PD78P0208 can have the same
memory map as used in mask ROM versions that have a different internal expansion RAM capacity.
For the mask ROM versions, IXS does not need to be set.
IXS is set with an 8-bit memory manipulation instruction.
RESET input sets IXS to 0AH.
Cautions 1. The internal expansion RAM size switching register (IXS) is only incorporated in the
µ PD780206, µ PD780208, and µ PD78P0208.
2. When using a mask ROM version µ PD780204, µ PD780204A, µ PD780205, µ PD780205A,
µ PD780206, µ PD780208, do not set a value other than those listed in Table 19-3 to IXS.
Figure 19-2. Format of Internal Expansion RAM Size Switching Register
Symbol 7 6 5
0 0 0
IXS
Table 19-3 lists the IXS setting values for a memory map equivalent to the mask ROM versions.
Table 19-3. Internal Expansion RAM Size Switching Register Setting Values
IXS is not incorporated in the µ PD780204, µ PD780204A, µ PD780205, and µ PD780205A.
However, if a write instruction to IXS is executed in the µ PD780204, µ PD780204A, µ PD780205, or
µ PD780205A, the operation is not affected.
374
CHAPTER 19 µ PD78P0208
4 3 2 1
IX IX IX
0
RAM3 RAM2 RAM1
Target Mask ROM Version
µ PD780204, 780204A
µ PD780205, 780205A
µ PD780206
µ PD780208
User's Manual U11302EJ4V0UM
0
Address After reset
IX
FFF4H 0AH
RAM0
IX IX IX
RAM3 RAM2 RAM1
1 0 1
1 1 0
Other than above
IXS Setting Value
0CH
0AH
R/W
W
Internal expansion RAM
IX
RAM0 capacity selection
0 1024 bytes
0 No internal expansion RAM (0 bytes)
Setting prohibited