NEC 26.1 Memory Size Switching Register

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CHAPTER 26 µ PD78P058F, 78P058FY
26.1 Memory Size Switching Register
In the µPD78P058F and 78P058FY, internal memory can be selected through the memory size select register
(IMS). The same memory mapping as that of mask ROM versions that have a different internal memory can be done
by setting IMS.
IMS is set with an 8-bit memory manipulation instruction.
RESET input sets IMS to CFH.
Figure 26-1. Memory Size Switching Register Format
Note When using the external device expansion function with µ PD78058F, 78P058F, 78058FY and 78P058FY,
the capacity of the internal ROM should be less than 56 Kbytes.
The IMS settings to give the same memory map as mask ROM versions are shown in Table 26-2.
Table 26-2. Examples of Memory Size Switching Register Settings
Relevant Mask ROM Version IMS Setting
µ PD78056F, 78056FY CCH
µ PD78058F, 78058FY CFH
7
RAM2
Symbol
IMS
6
RAM1
5
RAM0
4
0
3
ROM3
2
ROM2
1
ROM1
0
ROM0
Address
FFF0H CFH
After
Reset R/W
R/W
Internal ROM Capacity Selection ROM3ROM2 ROM1 ROM0
Setting prohibitedOther than above
Internal High-Speed RAM Capacity Selection RAM2 RAM1 RAM0
1024 bytes110
Setting prohibitedOther than above
1 56 Kbytes110
1 48 Kbytes100
1 60 Kbytes
111
Note