NEC PD78214 - Manual (Page 398)

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Chapter 13 Local Bus Interface Function
13
(b) Accessing External Memory
The refresh bus cycle is generated at the intervals specified with the refresh mode register (RFM).
Pseudo static RAM may malfunction if the access timing overlaps the refresh pulse output timing;
therefore, the
µPD78214 generates a refresh bus cycle of three clock pulses, synchronized with the bus
cycle.
Fig. 13-20 Pulse Refresh When External Memory Is Accessed
(a) When memory is read
(b) When memory is written
Refresh bus cycle Write cycle
f CLK
f CLK
ASTB
(output)
WR (output)
REFRQ
(output)
Refresh bus cycle Read cycle
t
CYC
t CYC
ASTB
(output)
RD (output)
REFRQ
(output)