nPCWAIT is the bus cycle extension signal for PCMCIA card access timing.
Section 5.1.7.2 PC Card Timing of the LH7A404 User's Guide covers this in detail, but here is a quick summary. If a PC card requires wait states beyond the maximum programable wait state value, the WEN bit can be set which allows the external device to assert nPCWAIT. While nPCWAIT is low the current bus transaction will be held beyond the programmed wait states until the external device deasserts the signal ending the current transaction.
I tried to dig up a timing diagram from the Sharp Data Sheet, but at this time they do not publish that signal on their PCMCIA timing waveforms.
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