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CHAPTER 18
µ
PD78F0034BS
Preliminary User’s Manual U16035EJ1V0UM
18.1 Memory Size Switching Register
The
µ
PD78F0034BS allows users to select the internal memory capacity using the memory size switching register
(IMS) so that the same memory map as that of the
µ
PD780021AS, 780022AS, 780023AS, 780024AS and
µ
PD780031AS, 780032AS, 780033AS, 780034AS with a different size of internal memory capacity can be achieved.
IMS is set by an 8-bit memory manipulation instruction.
RESET input sets IMS to CFH.
Caution
The initial value of IMS is “setting prohibited (CFH)”. Be sure to set the value of the relevant
mask ROM versions at initialization.
Figure 18-1. Format of 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
1
1
1
1
60 KB (setting prohibited)
Other than above
Setting prohibited
The IMS settings to obtain the same memory map as mask ROM versions are shown in Table 18-2.
Table 18-2. Memory Size Switching Register Settings
Target Mask ROM Versions
IMS Setting
µ
PD780021AS, 780031AS
42H
µ
PD780022AS, 780032AS
44H
µ
PD780023AS, 780033AS
C6H
µ
PD780024AS, 780034AS
C8H
Caution
When using the mask ROM versions, be sure to set the value indicated in Table 18-2 to IMS.