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CHAPTER 23 EXTERNAL DEVICE EXPANSION FUNCTION
(2) Separate bus mode
External devices are connected using independent address and data buses. This connection requires no
latches externally, resulting in reduction of external parts and area on the mounting board. In this mode,
ports 4 through 6 and port 8 are used for control of address/data, reafd/write strobe, wait as shown below.
Table 23-3. Pin Functions in Separate Bus Mode
Pin function in separate bus mode
Alternate function
Name
Function
AD0 to AD7
Multiplexed address/data bus
P40 to P47
A0 to A7
Lower Address bus
P80 to P87
A8 to A15
Upper Address bus
P50 to P57
RD
Read strobe signal
P64
WR
Write strobe signal
P65
WAIT
Wait signal
P66
Caution In this mode, the address strobe signal is not required to be used though it is output
from the ASTB/P67 pin. The output timings are shown in Figures 23-9 through 23-
12.
Table 23-4. State of Port 4 to Port 6 and Port 8 Pins in Separate Bus Mode
Ports and bits
Port 4
Port 8
Port 5
Port 6
Modes
0 to 7
0 to 7
0 1 2 3 4 5 6 7
0 to 3
4 to 7
Single-chip mode
Port
Port
Port
Port
Port
256-byte expansion mode
Data
Address
Port
Port
RD, WR, WAIT, (ASTB)
4-Kbyte expansion mode
Data
Address
Address
Port
Port
RD, WR, WAIT, (ASTB)
16-Kbyte expansion mode
Data
Address
Address
Port
Port
RD, WR, WAIT, (ASTB)
Full address mode
Data
Address
Address
Port
RD, WR, WAIT, (ASTB)
Cautions 1. When the external wait function is not used, the WAIT pin can be used as a port in all modes.
2. In this mode, the address strobe signal is not required to be used though it is output from the
ASTB/P67 pin. The output timings are shown in Figures 23-9 through 23-12.
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