Memory Size Switching Register ( Pd78P054); Memory Size Switching Register Format ( Pd78P054); Examples Of Memory Size Switching Register Settings ( Pd78P054) - NEC PD78052 User Manual

26.1 Memory Size Switching Register ( PD78P054)

The PD78P054 allows users to define its internal ROM and high-speed RAM sizes using the memory size
switching register (IMS), so that the same memory mapping as that of a mask ROM version with a different-size internal
ROM and high-speed RAM is possible. IMS is set with an 8-bit memory manipulation instruction.
RESET input sets IMS to C8H.
Figure 26-1. Memory Size Switching Register Format ( PD78P054)
Symbol 7 6 5
IMS RAM2 RAM1 RAM0
The IMS settings to give the same memory map as mask ROM versions are shown in Table 26-3.
Table 26-3. Examples of Memory Size Switching Register Settings ( PD78P054)
CHAPTER 26 PD78P054, 78P058
4 3 2 1 0
0 ROM3 ROM2 ROM1 ROM0
Relevant Mask ROM Version
PD78052
PD78053
PD78054
After
Address
Reset
FFF0H C8H
ROM3 ROM2 ROM1 ROM0 Internal ROM Capacity selection
0 1 0 0 16 Kbytes
0 1 1 0 24 Kbytes
1 0 0 0 32 Kbytes
Other than above Setting prohibited
RAM2 RAM1 RAM0 Internal High-Speed RAM Capacity Selection
0 1 0 512 bytes
1 1 0 1024 bytes
Other than above Setting prohibited
IMS Setting
44H
C6H
C8H
R/W
R/W
549