at28lv64b-20tc ATMEL Corporation, at28lv64b-20tc Datasheet - Page 3

• Manufacturer Part Number: at28lv64b-20tc
• Description: 64k 8k X 8 Low Voltage Cmos E2 Prom With Page Write And Software Data Protection
• Manufacturer: ATMEL Corporation

Device Operation
READ: The AT28LV64B is accessed like a static RAM.
When CE and OE are low and WE is high, the data stored
at the memory location determined by the address pins is
asserted on the outputs. The outputs are put in the high
impedance state when either CE or OE is high. This dual-
line control gives designers flexibility in preventing bus
contention in their systems.
BYTE WRITE: A low pulse on the WE or CE input with CE
or WE low (respectively) and OE high initiates a write cy-
cle. The address is latched on the falling edge of CE or
WE, whichever occurs last. The data is latched by the first
rising edge of CE or WE. Once a byte write has been
started, it will automatically time itself to completion. Once
a programming operation has been initiated and for the
duration of t
ing operation.
PAGE WRITE: T h e p a g e w r i t e o p e r a t i o n o f t h e
AT28LV64B allows 1 to 64-bytes of data to be written into
the device during a single internal programming period. A
page write operation is initiated in the same manner as a
byte write; the first byte written can then be followed by 1
to 63 additional bytes. Each successive byte must be writ-
ten within 100 s (t
limit is exceeded, the AT28LV64B will cease accepting
data and commence the internal programming operation.
All bytes during a page write operation must reside on the
same page as defined by the state of the A6 to A12 inputs.
For each WE high to low transition during the page write
operation, A6 to A12 must be the same.
The A0 to A5 inputs specify which bytes within the page
are to be written. The bytes may be loaded in any order
and may be altered within the same load period. Only
bytes which are specified for writing will be written; unnec-
essary cycling of other bytes within the page does not oc-
cur.
DATA POLLING: The AT28LV64B features DATA Polling
to indicate the end of a write cycle. During a byte or page
write cycle an attempted read of the last byte written will
result in the complement of the written data to be pre-
sented on I/O7. Once the write cycle has been completed,
true data is valid on all outputs, and the next write cycle
may begin. DATA Polling may begin at anytime during the
write cycle.
TOGGLE BIT: I n a d d i t i o n t o DATA P o l l i n g , t he
AT28LV64B provides another method for determining the
end of a write cycle. During the write operation, succes-
sive attempts to read data from the device will result in
I/O6 toggling between one and zero. Once the write has
completed, I/O6 will stop toggling and valid data will be
WC
, a read operation will effectively be a poll-
BLC
) of the previous byte. If the t
BLC
read. Reading the toggle bit may begin at any time during
the write cycle.
DATA PROTECTION: If precautions are not taken, inad-
vertent writes may occur during transitions of the host sys-
tem power supply. Atmel has incorporated both hardware
and software features that will protect the memory against
inadvertent writes.
HARDWARE PROTECTION: Hardware features protect
against inadvertent writes to the AT28LV64B in the follow-
ing ways: (a) V
1.8V (typical) the device will automatically time out 10 ms
(typical) before allowing a write; (b) write inhibit holding
any one of OE low, CE high or WE high inhibits write cy-
cles; (c) noise filter pulses of less than 15 ns (typical) on
the WE or CE inputs will not initiate a write cycle.
SOFTWARE DATA PROTECTION: A software-control-
led data protection feature has been implemented on the
AT28LV64B. Software data protection (SDP) helps pre-
vent inadvertent writes from corrupting the data in the de-
vice. SDP can prevent inadvertent writes during power-up
and power-down as well as any other potential periods of
system instability.
The AT28LV64B can only be written using the software
data protection feature . A series of three write commands
to specific addresses with specific data must be presented
to the device before writing in the byte or page mode. The
same three write commands must begin each write opera-
tion. All software write commands must obey the page
mode write timing specifications. The data in the 3-byte
command sequence is not written to the device; the ad-
dresses in the command sequence can be utilized just like
any other location in the device.
Any attempt to write to the device without the 3-byte se-
quence will start the internal write timers. No data will be
written to the device; however, for the duration of t
read operations will effectively be polling operations.
DEVICE IDENTIFICATION: A n e x t r a 6 4 - b y t e s o f
E
identification. By raising A9 to 12V
dress locations 7FC0H to 7FFFH, the additional bytes
may be written to or read from in the same manner as the
regular memory array.
2
PROM memory are available to the user for device
CC
power-on delay once V
AT28LV64B
0.5V and using ad-
CC
has reached
2-137
WC
,