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CHAPTER 18 EXTERNAL DEVICE EXPANSION FUNCTION
Preliminary User’s Manual U13420EJ2V0UM00
18.3 External Device Expansion Function Timing
Timing control signal output pins in the external memory expansion mode are as follows.
(1) RD pin (Alternate function: P64)
Read strobe output pin. The read strobe output pin is output in data accesses and instruction fetches from external
memory.
During internal memory access, the read strobe signal is not output (maintains high level).
(2) WR pin (Alternate function: P65)
Write strobe signal output pin. The write strobe signal is output in data access to external memory.
During internal memory access, the write strobe signal is not output (maintains high level)
(3) WAIT pin (Alternate function: P66)
External wait signal input pin.
When the external wait is not used, the WAIT pin can be used as an input/output port.
During internal memory access, the external wait signal is ignored.
(4) ASTB pin (Alternate function: P67)
Address strobe signal output pin. The address strobe signal is output regardless of data access and instruction
fetch from external memory. During internal memory access, the address strobe signal is not output.
(5) AD0 to AD7, A8 to A15 pins (Alternate function: P40 to P47, P50 to P57)
Address/data signal output pins. Valid signal is output or input during data accesses and instruction fetches from
external memory.
These signals change even during internal memory access (output values are undefined).
The timing charts are shown in Figures 18-4 to 18-7.
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