NEC PD78054(A) User Manual
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CHAPTER 22 EXTERNAL DEVICE EXPANSION FUNCTION
22.1 External Device Expansion Functions
The external device expansion functions connect external devices to areas other than the internal ROM, RAM,
and SFR. Connection of external devices uses ports 4 to 6. Ports 4 to 6 control address/data, read/write strobe,
wait, address strobe etc.
Table 22-1. Pin Functions in External Memory Expansion Mode
Pin function at external device connection
Alternate function
Name
Function
AD0 to AD7
Multiplexed address/data bus
P40 to P47
A8 to A15
Address bus
P50 to P57
RD
Read strobe signal
P64
WR
Write strobe signal
P65
WAIT
Wait signal
P66
ASTB
Address strobe signal
P67
Table 22-2. State of Ports 4 to 6 Pins in External Memory Expansion Mode
Ports and bits
Port 4
Port 5
Port 6
Modes
0-7
0 1 2 3 4 5 6 7
0-3
4-7
Single-chip mode
Port
Port
Port
Port
256-byte expansion mode
Address/data
Port
Port
RD, WR, WAIT, ASTB
4K-byte expansion mode
Address/data
Address
Port
Port
RD, WR, WAIT, ASTB
16K-byte expansion mode
Address/data
Address
Port
Port
RD, WR, WAIT, ASTB
Full address mode
Address/data
Address
Port
RD, WR, WAIT, ASTB
Caution
When the external wait function is not used, the WAIT pin can be used as a port in all modes.