FT28HC256
RESETTING SOFTWARE DATA PROTECTION
Figure 8. Reset Software Data Protection Timing Sequence
V
CC
AAA
5555
55
2AAA
80
5555
AA
5555
55
2AAA
20
5555
Standard
Operating
Mode
Data
Address
t
WC
CE
WE
Figure 9. Write Sequence for resetting Software
Data Protection
In the event the user wants to deactivate the software
data protection feature for testing or reprogramming in
an EEPROM programmer, the following six step algo-
rithm will reset the internal protection circuit. After t
the FT28HC256 will be in standard operating mode.
,
WC
Write Data AA
to Address
5555
Note: Once initiated, the sequence of write operations
should not be interrupted.
Write Data 55
to Address
2AAA
SYSTEM CONSIDERATIONS
Because the FT28HC256 is frequently used in large
memory arrays, it is provided with a two line control
architecture for both read and write operations. Proper
usage can provide the lowest possible power dissipa-
tion, and eliminate the possibility of contention where
multiple I/O pins share the same bus.
Write Data 80
to Address
5555
Write Data AA
to Address
5555
To gain the most benefit, it is recommended that CE be
decoded from the address bus and be used as the pri-
mary device selection input. Both OE and WE would
then be common among all devices in the array. For a
read operation, this assures that all deselected devices
are in their standby mode, and that only the selected
device(s) is/are outputting data on the bus.
Write Data 55
to Address
2AAA
Because the FT28HC256 has two power modes ,
standby and active, proper decoupling of the memory
array is of prime concern. Enabling CE will cause tran-
sient current spikes. The magnitude of these spikes is
dependent on the output capacitive loading of the l/Os.
Therefore, the larger the array sharing a common bus,
the larger the transient spikes. The voltage peaks
associated with the current transients can be sup-
pressed by the proper selection and placement of
decoupling capacitors. As a minimum, it is recommended
Write Data 20
to Address
5555
After t
,
WC
Re-Enters
Unprotected
State
Characteristics subject to change without notice. 7 of 23
REV 1.0