4 Mbit SPI Serial Flash
SST25VF040B
Data Sheet
Hold Operation
The HOLD# pin is used to pause a serial sequence under-
way with the SPI flash memory without resetting the clock-
ing sequence. To activate the HOLD# mode, CE# must be
in active low state. The HOLD# mode begins when the
SCK active low state coincides with the falling edge of the
HOLD# signal. The HOLD mode ends when the HOLD#
signal’s rising edge coincides with the SCK active low state.
coincide with the SCK active low state, then the device
exits in Hold mode when the SCK next reaches the active
low state. See Figure 4 for Hold Condition waveform.
Once the device enters Hold mode, SO will be in high-
impedance state while SI and SCK can be VIL or VIH.
If CE# is driven active high during a Hold condition, it resets
the internal logic of the device. As long as HOLD# signal is
low, the memory remains in the Hold condition. To resume
communication with the device, HOLD# must be driven
active high, and CE# must be driven active low. See Figure
24 for Hold timing.
If the falling edge of the HOLD# signal does not coincide
with the SCK active low state, then the device enters Hold
mode when the SCK next reaches the active low state.
Similarly, if the rising edge of the HOLD# signal does not
SCK
HOLD#
Active
Hold
Active
Hold
Active
1295 HoldCond.0
FIGURE 4: Hold Condition Waveform
TABLE 2: Conditions to execute Write-Status-
Register (WRSR) Instruction
Write Protection
SST25VF040B provides software Write protection. The
Write Protect pin (WP#) enables or disables the lock-down
function of the status register. The Block-Protection bits
(BP3, BP2, BP1, BP0, and BPL) in the status register pro-
vide Write protection to the memory array and the status
register. See Table 4 for the Block-Protection description.
WP#
BPL
1
Execute WRSR Instruction
Not Allowed
L
L
0
Allowed
H
X
Allowed
T2.0 1295
Write Protect Pin (WP#)
The Write Protect (WP#) pin enables the lock-down func-
tion of the BPL bit (bit 7) in the status register. When WP#
is driven low, the execution of the Write-Status-Register
(WRSR) instruction is determined by the value of the BPL
bit (see Table 2). When WP# is high, the lock-down func-
tion of the BPL bit is disabled.
©2009 Silicon Storage Technology, Inc.
S71295-05-000
10/09
5
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