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17.1 Memory Size Switching Register (IMS)
The internal memory capacity of the µ PD178F054 can be changed using the memory size switching register (IMS).
By using this register, the memory of the µ PD178F054 can be mapped in the same manner as a mask ROM version
with a different internal memory capacity.
IMS is set with an 8-bit memory manipulation instruction.
Reset input sets this register to CFH.
Be sure to set IMS to C6H or C8H.
Figure 17-1. Format of Memory Size Switching Register (IMS)
Symbol
7
6
5
IMS
RAM2
RAM1
RAM0
RAM2 RAM1 RAM0
0
1
0
1
1
0
Other than above
ROM3 ROM2 ROM1 ROM0
0
1
1
1
0
0
Other than above
Table 17-2 shows the setting of IMS to perform the same memory mapping as that of a mask ROM version.
Table 17-2. Set Value of Memory Size Switching Register
CHAPTER 17 µ PD178F054
4
3
2
1
0
0
ROM3
ROM2
ROM1
ROM0
Selection of internal high-speed RAM capacity
512 bytes
1024 bytes
Setting prohibited
0
24 KB
0
32 KB
Setting prohibited
Targeted Model
µ PD178053
µ PD178054
User's Manual U15104EJ2V0UD
Address
After reset
R/W
FFF0H
CFH
R/W
Selection of internal ROM capacity
Set Value of IMS
C6H
C8H
221
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