12
P/N:PM0439
MX29F400T/B
REV. 1.6, NOV. 12, 2001
Q5
Exceeded Timing Limits
Q5 will indicate if the program or erase time has ex-
ceeded the specified limits(internal pulse count). Under
these conditions Q5 will produce a "1". This time-out
condition indicates that the program or erase cycle was
not successfully completed. Data Polling and Toggle Bit
are the only operating functions of the device under this
condition.
If this time-out condition occurs during sector erase op-
eration, it specifies that a particular sector is bad and it
may not be reused. However, other sectors are still func-
tional and may be used for the program or erase opera-
tion. The device must be reset to use other sectors.
Write the Reset command sequence to the device, and
then execute program or erase command sequence. This
allows the system to continue to use the other active
sectors in the device.
If this time-out condition occurs during the chip erase
operation, it specifies that the entire chip is bad or com-
bination of sectors are bad.
If this time-out condition occurs during the byte program-
ming operation, it specifies that the entire sector con-
taining that byte is bad and this sector maynot be re-
used, (other sectors are still functional and can be re-
used).
The time-out condition may also appear if a user tries to
program a non blank location without erasing. In this
case the device locks out and never completes the Au-
tomatic Algorithm operation. Hence, the system never
reads a valid data on Q7 bit and Q6 never stops tog-
gling. Once the Device has exceeded timing limits, the
Q5 bit will indicate a "1". Please note that this is not a
device failure condition since the device was incorrectly
used.
DATA PROTECTION
The MX29F400T/B is designed to offer protection against
accidental erasure or programming caused by spurious
system level signals that may exist during power transi-
tion. During power up the device automatically resets
the state machine in the Read mode. In addition, with
its control register architecture, alteration of the memory
contents only occurs after successful completion of spe-
cific command sequences. The device also incorpo-
rates several features to prevent inadvertent write cycles
TEMPORARY SECTOR UNPROTECT
This feature allows temporary unprotection of previously
protected sector to change data in-system. The Tempo-
rary Sector Unprotect mode is activated by setting the
RESET pin to VID(11.5V-12.5V). During this mode, for-
merly protected sectors can be programmed or erased
as un-protected sector. Once VID is remove from the
RESET pin,all the previously protected sectors are pro-
tected again.
Q3
Sector Erase Timer
After the completion of the initial sector erase command
sequence, the sector erase time-out will begin. Q3 will
remain low until the time-out is complete. Data Polling
and Toggle Bit are valid after the initial sector erase com-
mand sequence.
If Data Polling or the Toggle Bit indicates the device has
been written with a valid erase command, Q3 may be
used to determine if the sector erase timer window is
still open. If Q3 is high ("1") the internally controlled
erase cycle has begun; attempts to write subsequent
commands to the device will be ignored until the erase
operation is completed as indicated by Data Polling or
Toggle Bit. If Q3 is low ("0"), the device will accept
additional sector erase commands. To insure the com-
mand has been accepted, the system software should
check the status of Q3 prior to and following each sub-
sequent sector erase command. If Q3 were high on the
second status check, the command may not have been
accepted.
WRITE PULSE "GLITCH" PROTECTION
Noise pulses of less than 5ns(typical) on CE or WE will
not initiate a write cycle.
LOGICAL INHIBIT
Writing is inhibited by holding any one of OE = VIL, CE
= VIH or WE = VIH. To initiate a write cycle CE and WE
must be a logical zero while OE is a logical one.
POWER SUPPLY DECOUPLING
In order to reduce power switching effect, each device
should have a 0.1uF ceramic capacitor connected be-
tween its VCC and GND.
resulting from VCC power-up and power-down transition
or system noise.