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19.1 External Device Expansion Functions
The external device expansion functions are intended to connect external devices to areas other than the internal
ROM, RAM and SFR. Connection of external devices uses port 4 to port 6. Port 4 to port 6 control address/data,
read/write strobe, wait, address strobe, etc.
External
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Expansion Mode
Single-chip mode
256 bytes expansion Address/Data
mode
4 Kbytes expansion
mode
16 Kbytes expansion
mode
Full-address mode
Caution
CHAPTER 19 EXTERNAL DEVICE EXPANSION FUNCTION
CHAPTER 19 EXTERNAL DEVICE EXPANSION FUNCTION
Table 19-1. Pin Functions in External Memory Expansion Mode
Pin Function at External Device Connection
Name
AD0 to AD7
A8 to A15
RD
WR
WAIT
ASTB
Table 19-2. State of Port 4 to Port 6 Pins in External Memory Expansion Mode
Port
Port 4
0 to 7
Port
Address/Data
Address/Data
Address/Data
When the external wait function is not used, the WAIT pin can be used as a port in all modes.
Function
Multiplexed address/data bus
Address bus
Read strobe signal
Write strobe signal
Wait signal
Address strobe signal
Port 5
0
1
2
3
4
5
Port
Port
Address
Port
Address
Address
Alternate
Function
P40 to P47
P50 to P57
P64
P65
P66
P67
Port 6
6
7
0
1
2
3
Port
Port
Port
Port
Port
Port
4
5
6
7
RD, WR, WAIT, ASTB
RD, WR, WAIT, ASTB
RD, WR, WAIT, ASTB
RD, WR, WAIT, ASTB
473
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