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AT28C64B Datasheet(PDF) 3 Page - ATMEL Corporation

Part No. AT28C64B
Description  64K (8K x 8) Parallel EEPROM with Page Write and Software Data Protection
Download  13 Pages
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Maker  ATMEL [ATMEL Corporation]
Homepage  http://www.atmel.com
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AT28C64B Datasheet(HTML) 3 Page - ATMEL Corporation

 
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AT28C64B
3
Device Operation
READ: The AT28C64B 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 con-
tention 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 cycle.
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 pro-
gramming operation has been initiated and for the duration
of t
WC , a r ead o perati on wil l effec t ive l y be a p o llin g
operation.
PAGE WRITE: The page write operation of the AT28C64B
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;
after the first byte is written, it can then be followed by 1 to
63 additional bytes. Each successive byte must be loaded
within 150 µs (t
BLC) of the previous byte. If the tBLC limit is
exceeded, the AT28C64B 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 opera-
tion, 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; unnecessary
cycling of other bytes within the page does not occur.
DATA POLLING: The AT28C64B 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 presented
on I/O
7. 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 any time during the write
cycle.
TOGGLE BIT: In addition to DATA Polling, the AT28C64B
provides another method for determining the end of a write
cycle. During the write operation, successive attempts to
read data from the device will result in I/O6 toggling
between one and zero. Once the write has completed, I/O
6
will stop toggling, and valid data will be read. Toggle bit
reading 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 DATA PROTECTION: Hardware features
protect against inadvertent writes to the AT28C64B in the
following ways: (a) V
CC sense – if VCC is below 3.8V (typi-
cal), the write function is inhibited; (b) V
CC power-on delay
– once V
CC has reached 3.8V, the device will automatically
time out 5 ms (typical) before allowing a write; (c) write
inhibit – holding any one of OE low, CE high, or WE high
inhibits write cycles; and (d) 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 controlled
data protection feature has been implemented on the
AT28C64B. When enabled, the software data protection
(SDP), will prevent inadvertent writes. The SDP feature
may be enabled or disabled by the user; the AT28C64B is
shipped from Atmel with SDP disabled.
SDP is enabled by the user issuing a series of three write
commands in which three specific bytes of data are written
to three specific addresses (refer to the “Software Data
Protection Algorithm” diagram in this datasheet). After writ-
ing the 3-byte command sequence and waiting t
WC, the
entire AT28C64B will be protected against inadvertent
writes. It should be noted that even after SDP is enabled,
the user may still perform a byte or page write to the
AT28C64B by preceding the data to be written by the same
3-byte command sequence used to enable SDP.
Once set, SDP remains active unless the disable command
sequence is issued. Power transitions do not disable SDP,
and SDP protects the AT28C64B during power-up and
power-down conditions. All command sequences must
conform to the page write timing specifications. The data in
the enable and disable command sequences is not actually
written into the device; their addresses may still be written
with user data in either a byte or page write operation.
After setting SDP, any attempt to write to the device without
the 3-byte command sequence will start the internal write
timers. No data will be written to the device. However, for
the duration of t
WC, read operations will effectively be poll-
ing operations.
DEVICE IDENTIFICATION: An extra 64 bytes of EEPROM
memory are available to the user for device identification.
By raising A9 to 12V
± 0.5V and using address locations
1FC0H to 1FFFH, the additional bytes may be written to or
read from in the same manner as the regular memory
array.


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