External Device Expansion Function Timing - NEC 78014Y Series User Manual

19.3 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 signal output pin. The read strobe signal is output in data access and instruction fetch 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 function 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. Timing signal is always output regardless of the data access or instruction fetch
from external memory. The address strobe signal is also output when the internal memory is accessed.
(5) AD0 to AD7, A8 to A15 pins (Alternate function: P40 to P47, P50 to P57)
Address/data signal output pins. Valid signals are output or input during instruction fetch and data access from/
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to external memory.
These signals change when the internal memory is accessed (output values are undefined).
Timing charts are shown in Figures 19-3 to 19-6.
CHAPTER 19 EXTERNAL DEVICE EXPANSION FUNCTION
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