UPD784938 Datasheet, PDF (672/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 28 µPD78F4938 PROGRAMMING
28.1 Internal Memory Size Switching Register (IMS)
IMS is a register to prevent a certain part of the internal memory from being used by software. By setting the IMS, it
is possible to establish a memory map that is the same as that of mask ROM version with a different internal memory (ROM,
RAM) with capacity.
IMS is set with an 8-bit memory manipulation instruction.
RESET input sets IMS to FFH.
Figure 28-1. Internal Memory Size Switching Register (IMS) Format
Address 0FFFCH After reset FFH W
Symbol
7
6
5
4
3
IMS
1
1
ROM1 ROM0
1
2
1
0
1
RAM1
RAM0
ROM1
0
0
1
1
ROM0
0
1
0
1
Internal ROM Capacity Selection
256 Kbytes
96 Kbytes
128 Kbytes
192 Kbytes
RAM1
0
0
1
1
RAM0
0
1
0
1
Internal RAM Capacity Selection
10,240 bytes
5,120 bytes
6,656 bytes
8,192 bytes
Caution IMS is not available for mask ROM versions (µPD784935, 784936, 784937, and 784938).
The IMS settings to create the same memory map as mask ROM versions are shown in Table 28-2.
Table 28-2. Internal Memory Size Switching Register (IMS) Settings
Relevant Mask ROM Version
IMS Setting
µPD784935
DDH
µPD784936
EEH
µPD784937
FFH
µPD784938
CCH
672
Preliminary User’s Manual U13987EJ1V0UM00