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(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.
Name
AD0 to AD7
A0 to A7
A8 to A15
RD
WR
WAIT
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
Modes
Single-chip mode
256-byte expansion mode
4-Kbyte expansion mode
16-Kbyte expansion mode
Full address mode
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.
528
CHAPTER 23 EXTERNAL DEVICE EXPANSION FUNCTION
Table 23-3. Pin Functions in Separate Bus Mode
Pin function in separate bus mode
Function
Multiplexed address/data bus
Lower Address bus
Upper Address bus
Read strobe signal
Write strobe signal
Wait signal
Port 4
Port 8
0 to 7
0 to 7
Port
Port
Data
Address
Data
Address
Data
Address
Data
Address
Alternate function
P40 to P47
P80 to P87
P50 to P57
P64
P65
P66
Port 5
0
1
2
3
4
5
6
7
0 to 3
Port
Port
Port
Port
Address
Port
Port
Address
Port
Port
Address
Port
Port 6
4 to 7
Port
RD, WR, WAIT, (ASTB)
RD, WR, WAIT, (ASTB)
RD, WR, WAIT, (ASTB)
RD, WR, WAIT, (ASTB)
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