NEC PD78P078 User Manual
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CHAPTER 23 EXTERNAL DEVICE EXPANSION FUNCTION
23.2 External Device Expansion Function Control Register
The external device expansion function is controlled by the memory expansion mode register (MM) and internal
memory size switching register (IMS).
(1) Memory expansion mode register (MM)
MM sets the wait count and external expansion area, and also sets the input/output of port 4.
MM is set with 1- or 8-bit memory manipulation instruction.
RESET input sets this register to 10H.
Figure 23-2. Memory Expansion Mode Register Format
Notes 1. This can be used only in the separate bus mode. In the multiplexed bus mode, these pins enter
the port mode.
2. The full address mode allows external expansion to the entire 64-Kbyte address space except
for the internal ROM, RAM, and SFR areas and the reserved area.
Remark
P60 to P63 enter the port mode without regard to the mode (single-chip mode or memory
expansion mode).
7
0
Symbol
MM
6
0
5
PW1
4
PW0
3
0
2
MM2
1
MM1
0
MM0
Address
FFF8H
10H
After
Reset
R/W
R/W
MM2
MM1
MM0
Single-chip/
Memory Expansion
Mode Selection
Memory Expansion
Mode Selection
P40 to P47, P50 to P57, P64 to P67, P80 to P87 Pin state
P40 to P47 P80 to P87 P50 to P53 P54, P55
P56, P57
P64 to P67
0
0
0
0
0
1
0
1
1
1
0
0
1
0
1
1
1
1
Single-chip mode
256-byte
mode
mode
4-Kbyte
mode
mode
16-Kbyte
mode
mode
Full
address
mode
address
mode
Note 2
Memory
expansion
mode
expansion
mode
Port
mode
mode
Input
Output
Port mode
Port mode
Port mode
Port mode
AD0 to AD7 A0 to A7
Note 1
A8 to A11
A12, A13
A14, A15
P64 = RD
P65 = WR
P66 = WAIT
P67 = ASTB
Other than above
Setting prohibited
PW1
PW0
0
0
0
1
1
0
1
1
Wait Control
No wait
Wait (one wait state insertion)
Setting prohibited
Wait control by external wait pin