CHAPTER 25
µµµµ
PD78F0124
Preliminary User’s Manual U16315EJ1V0UD
385
25.1 Internal Memory Size Switching Register
The
µ
PD78F0124 allows users to select the internal memory capacity using the internal memory size switching
register (IMS) so that the same memory map as that of the mask ROM versions with a different internal memory
capacity can be achieved.
IMS is set by an 8-bit memory manipulation instruction.
RESET input sets IMS to CFH.
Caution
Be sure to set the value of the relevant mask ROM version at initialization.
Figure 25-1. Format of Internal Memory Size Switching Register (IMS)
Address: FFF0H After reset: CFH R/W
Symbol
7
6
5
4
3
2
1
0
IMS
RAM2
RAM1
RAM0
0
ROM3
ROM2
ROM1
ROM0
RAM2
RAM1
RAM0
Internal high-speed RAM capacity selection
0
1
0
512 bytes
1
1
0
1024 bytes
Other than above
Setting prohibited
ROM3
ROM2
ROM1
ROM0
Internal ROM capacity selection
0
0
1
0
8 KB
0
1
0
0
16 KB
0
1
1
0
24 KB
1
0
0
0
32 KB
Other than above
Setting prohibited
The IMS settings required to obtain the same memory map as mask ROM versions are shown in Table 25-2.
Table 25-2. Internal Memory Size Switching Register Settings
Target Mask ROM Versions
IMS Setting
µ
PD780121
42H
µ
PD780122
44H
µ
PD780123
C6H
µ
PD780124
C8H
Caution
When using a mask ROM version, be sure to set the value indicated in Table 25-2 to IMS.