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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.