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28F320D18
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45
7.3.3
Using Asynchronous Page Mode
Upon power-up or return from reset, the device defaults to asynchronous page mode, with a page
size of four words. This read mode is only supported from the main blocks, and is not supported
from other locations within the device, such as the parameter blocks, the device identification
codes, query information, and status register.
In asynchronous page mode, CLK is ignored and ADV# must be held low throughout the page
access. With ADV# low, the internal address latch is open, allowing new page accesses. The initial
valid address will store four words of data in the internal page buffer. Each word is then output onto
the data lines by toggling address lines A
1-0
.
If an application only uses the asynchronous page mode capability, CLK and ADV# can be tied to
V
SS
, as shown in
Figure 20, “Different Clock Options” on page 48
. This shows an ideal, glueless
interface. If the processor does not provide any or all of these signals, some glue logic may be
required. More information on signal generation is covered later in this section. Grounding CLK
and ADV# will minimize the power consumed by these two pins and will simplify the interface,
making it compatible with standard flash memory and industry standard page mode ROMs. With
the ADV# signal tied low, the addresses cannot be latched into the device. This means that
addresses must stay valid throughout the entire read or write cycle, until CE# or either WE# or OE#
go high.
Figure 17, “Asynchronous Page Mode Read Waveform” on page 46
, shows an
asynchronous read timing diagram with ADV# held low. Note that address lines A
1-0
are toggled to
clock out the data.
Figure 15. WAIT# Pin Connection Using Multiple Flash Memory Components
Burst CPU
or System
Wait-State Logic
1.8 Volt Dual-Plane
Flash Memory
WAIT#
1.8 Volt Dual-Plane
Flash Memory
WAIT#
READY#
Wire OR’d WAIT#
Data
DQ
15-0
DQ
15-0
x16