Memory Size Switching Register (Ims) - NEC mPD780852 Series Preliminary User's Manual

22.1 Memory Size Switching Register (IMS)

The µ PD78F0852 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 mask ROM version with a different size of internal memory capacity
can be achieved.
IMS is set with 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
1
Other than above
ROM3
1
1
Other than above
The IMS settings to obtain the same memory map as the mask ROM version are shown in Table 22-2.
276
CHAPTER 22 µ PD78F0852
6 5 4
RAM1 RAM0 0
RAM1 RAM0
1 0 1,024 bytes
Setting prohibited
ROM2 ROM1 ROM0
0 0 0
0 1 0
Table 22-2. Memory Size Switching Register Settings
Mask ROM Version
µ PD780851(A)
µ PD780852(A)
Preliminary User's Manual U14581EJ3V0UM00
3 2
ROM3 ROM2
Internal High-Speed RAM Capacity Selection
Internal ROM Capacity Selection
32 Kbytes
40 Kbytes
Setting prohibited
IMS Setting
C8H
CAH
1 0
ROM1 ROM0