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User’s Manual U12697EJ3V0UM
CHAPTER 23 LOCAL BUS INTERFACE FUNCTIONS
23.1 External Memory Expansion Function
The external memory expansion function connects external memory to the areas other than the internal ROM, RAM,
and SFR.
A time-divided address/data bus is used to connect external memory. A 256-byte expansion mode and a 1 MB
expansion mode are supported in the external memory expansion function.
When external memory is connected, ports 4 to 6 are used. Ports 4 to 6 control address/data and read/write strobes,
and wait and address strobes, etc.
Table 23-1. Pin Functions in External Memory Expansion Mode
Pin Functions When External Device Connected
Alternate
Name
Function
Functions
AD0 to AD7
Multiplexed address/data bus
P40 to P47
A8 to A15
Middle address bus
P50 to P57
A16 to A19
High address bus
P60 to P63
RD
Read strobe
P64
WR
Write strobe
P65
WAIT
Wait signal
P66
ASTB
Address strobe
P67
Table 23-2. Pin States in Ports 4 to 6 in External Memory Expansion Mode
Port
Port 4
Port 5
Port 6
External Expansion Mode
0 to 7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
Single-chip mode
Port
Port
Port
256 KB expansion mode
Address/data
Address
Address Port
RD, WR, WAIT, ASTB
1 MB expansion mode
Address/data
Address
Address
RD, WR, WAIT, ASTB
Caution When the external wait function is not used, the WAIT pin can be used as the port in all of the
modes.
