External Device Expansion Function Control Register; Memory Expansion Mode Register Format - NEC PD78076 User Manual

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
Symbol 7 6 5
MM 0 0 PW1
MM2 MM1 MM0
0 0 0
0 0 1
0 1 1
1 0 0
1 0 1
1 1 1
Other than above
PW1 PW0
0 0 No wait
0 1 Wait (one wait state insertion)
1 0 Setting prohibited
1 1 Wait control by external wait pin
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).
CHAPTER 23 EXTERNAL DEVICE EXPANSION FUNCTION
4 3 2 1
PW0 0 MM2 MM1
Single-chip/
Memory Expansion
Mode Selection P40 to P47 P80 to P87 P50 to P53 P54, P55
Port
Single-chip mode
mode
256-byte
mode
4-Kbyte
mode
Memory
expansion
AD0 to AD7 A0 to A7
mode
16-Kbyte
mode
Full
address
Note 2
mode
Setting prohibited
After
Address
0
Reset
FFF8H 10H
MM0
P40 to P47, P50 to P57, P64 to P67, P80 to P87 Pin state
Input
Port mode
Output
Note 1
A8 to A11
Wait Control
R/W
R/W
P56, P57 P64 to P67
Port mode
P64 = RD
Port mode
P65 = WR
P66 = WAIT
Port mode P67 = ASTB
A12, A13
A14, A15
531