Registers Controlling External Bus Interface; Format Of Memory Expansion Mode Register (Mem) - NEC 78K0 User Manual

5.2

Registers Controlling External Bus Interface

The external bus interface is controlled by the following two registers.
• Memory expansion mode register (MEM)
• Memory expansion wait setting register (MM)
(1) Memory expansion mode register (MEM)
MEM sets the external expansion area.
MEM is set by a 1-bit or 8-bit memory manipulation instruction.
RESET input clears MEM to 00H.
Figure 5-2. Format of Memory Expansion Mode Register (MEM)
Address: FF47H After reset: 00H
Symbol 7
MEM 0
MM2 MM1
0
0
1
1
1
Other than above
132
CHAPTER 5 EXTERNAL BUS INTERFACE
R/W
6 5 4
0 0 0
MM0 Single-chip/memory
expansion mode selection P40 to P47 P50 to P53 P54, P55
0 0 Single-chip mode
1 1 Memory
expansion
Note
mode
0 0
0 1
1 1
Setting prohibited
User's Manual U15947EJ2V0UD
3 2 1
0 MM2 MM1
P40 to P47, P50 to P57, P64 to P67 pin state
Port mode
256-byte AD0 to Port mode
mode AD7
*
4 KB A8 to A11
mode
16 KB
mode
Full-address
mode
0
MM0
P56, P57 P64 to P67
P64 = RD
P65 = WR
P66 = WAIT
Port mode
P67 = ASTB
A12, A13 Port mode
A14, A15