Memory Size Switching Register - NEC mPD780973 Series Preliminary User's Manual

22.1 Memory Size Switching Register

The µ PD78F0974 allow 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 PD780973(A) with a different size of internal memory capacity can be
achieved.
IMS is set by using an 8-bit memory manipulation instruction.
RESET input sets IMS to CFH.
Figure 22-1. Memory Size Switching Register (IMS) Format
Address: FFF0H After Reset: CFH R/W
Symbol 7
IMS RAM2
RAM2
0
1
Other than above
ROM3
0
1
Other than above
The IMS settings to obtain the same memory map as the µ PD780973(A) are shown in Table 22-2.
With the µ PD780973(A), IMS must be set to 06H.
Caution
258
CHAPTER 22 µ PD78F0974
6 5 4
RAM1 RAM0 0
RAM1 RAM0
0 0 768 bytes
1 0 1024 bytes
Setting prohibited
ROM2 ROM1 ROM0
1 1 0
0 0 0
Table 22-2. Memory Size Switching Register Settings
Product
µ PD780973(A)
3 2
ROM3 ROM2
Internal High-Speed RAM Capacity Selection
Internal ROM Capacity Selection
24 Kbytes
32 Kbytes
Setting prohibited
IMS Setting
06H
1 0
ROM1 ROM0