Features
• Fast Read Access Time – 70 ns
• Automatic Page Write Operation
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– Internal Address and Data Latches for 64 Bytes
– Internal Control Timer
Fast Write Cycle Times
– Page Write Cycle Time: 3 ms or 10 ms Maximum
– 1 to 64-byte Page Write Operation
Low Power Dissipation
– 80 mA Active Current
– 3 mA Standby Current
Hardware and Software Data Protection
DATA Polling for End of Write Detection
High Reliability CMOS Technology
– Endurance: 104 or 105 Cycles
– Data Retention: 10 Years
Single 5V ± 10% Supply
CMOS and TTL Compatible Inputs and Outputs
JEDEC Approved Byte-wide Pinout
Full Military, Commercial, and Industrial Temperature Ranges
Green (Pb/Halide-free) Packaging Option
256 (32K x 8)
High-speed
Parallel
EEPROM
AT28HC256
1. Description
The AT28HC256 is a high-performance electrically erasable and programmable readonly memory. Its 256K of memory is organized as 32,768 words by 8 bits. Manufactured with Atmel’s advanced nonvolatile CMOS technology, the AT28HC256 offers
access times to 70 ns with power dissipation of just 440 mW. When the AT28HC256
is deselected, the standby current is less than 5 mA.
The AT28HC256 is accessed like a Static RAM for the read or write cycle without the
need for external components. The device contains a 64-byte page register to allow
writing of up to 64 bytes simultaneously. During a write cycle, the address and 1 to 64
bytes of data are internally latched, freeing the addresses and data bus for other operations. Following the initiation of a write cycle, the device will automatically write the
latched data using an internal control timer. The end of a write cycle can be detected
by DATA Polling of I/O7. Once the end of a write cycle has been detected a new
access for a read or write can begin.
Atmel’s 28HC256 has additional features to ensure high quality and manufacturability.
The device utilizes internal error correction for extended endurance and improved
data retention characteristics. An optional software data protection mechanism is
available to guard against inadvertent writes. The device also includes an extra
64 bytes of EEPROM for device identification or tracking.
0007J–PEEPR–04/05
AT28HC256
3. Block Diagram
4. Device Operation
4.1
Read
The AT28HC256 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 system.
4.2
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 programming operation has been initiated
and for the duration of tWC, a read operation will effectively be a polling operation.
4.3
Page Write
The page write operation of the AT28HC256 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 written within 150 µs (tBLC) of the previous byte. If the
tBLC limit is exceeded the AT28C256 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 - A14 inputs. That is, for each WE high to low transition during the page write operation, A6 - A14 must be the same.
The A0 to A5 inputs are used to 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.
4.4
DATA Polling
The AT28HC256 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/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.
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0007J–PEEPR–04/05
