Features
•
Fast Read Access Time – 70 ns
•
Automatic Page Write Operation
– 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: 10
4
or 10
5
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 read-
only memory. Its 256K of memory is organized as 32,768 words by 8 bits. Manufac-
tured 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 oper-
ations. 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
2. Pin Configurations
Pin Name
A0 - A14
CE
OE
WE
I/O0 - I/O7
NC
DC
Function
Addresses
Chip Enable
Output Enable
Write Enable
Data Inputs/Outputs
No Connect
Don’t Connect
2.1
28-lead TSOP Top View
OE
A11
A9
A8
A13
WE
VCC
A14
A12
A7
A6
A5
A4
A3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
A10
CE
I/O7
I/O6
I/O5
I/O4
I/O3
GND
I/O2
I/O1
I/O0
A0
A1
A2
2.3
32-pad LCC, 32-lead PLCC Top View
A7
A12
A14
DC
VCC
WE
A13
Note:
PLCC package pins 1 and 17 are Don’t Connect.
2.2
28-lead PGA Top View
2.4
28-lead Cerdip/PDIP/Flatpack/SOIC –
Top View
A14
A12
A7
A6
A5
A4
A3
A2
A1
A0
I/O0
I/O1
I/O2
GND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
VCC
WE
A13
A8
A9
A11
OE
A10
CE
I/O7
I/O6
I/O5
I/O4
I/O3
2
AT28HC256
0007J–PEEPR–04/05
I/O1
I/O2
GND
DC
I/O3
I/O4
I/O5
14
15
16
17
18
19
20
A6
A5
A4
A3
A2
A1
A0
NC
I/O0
5
6
7
8
9
10
11
12
13
4
3
2
1
32
31
30
29
28
27
26
25
24
23
22
21
A8
A9
A11
NC
OE
A10
CE
I/O7
I/O6
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 t
WC
, 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 (t
BLC
) of the previous byte. If the
t
BLC
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 dur-
ing 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.
3
0007J–PEEPR–04/05
4.5
Toggle Bit
In addition to DATA Polling the AT28HC256 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/O6 will stop
toggling and valid data will be read. Testing the toggle bit may begin at any time during the
write cycle.
4.6
Data Protection
If precautions are not taken, inadvertent writes to any 5-volt-only nonvolatile memory may
occur during transition of the host system power supply. Atmel has incorporated both hard-
ware and software features that will protect the memory against inadvertent writes.
4.6.1
Hardware Protection
Hardware features protect against inadvertent writes to the AT28HC256 in the following ways:
(a) V
CC
sense – if V
CC
is below 3.8V (typical) 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 AT28HC256.
When enabled, the software data protection (SDP), will prevent inadvertent writes. The SDP
feature may be enabled or disabled by the user; the AT28HC256 is shipped from Atmel with
SDP disabled.
SDP is enabled by the host system issuing a series of three write commands; three specific
bytes of data are written to three specific addresses (refer to “Software Data Protection” algo-
rithm). After writing the 3-byte command sequence and after t
WC
the entire AT28HC256 will be
protected against inadvertent write operations. It should be noted, that once protected the host
may still perform a byte or page write to the AT28HC256. This is done by preceding the data to
be written by the same 3-byte command sequence.
Once set, SDP will remain active unless the disable command sequence is issued. Power
transitions do not disable SDP and SDP will protect the AT28HC256 during power-up and
power-down conditions. All command sequences must conform to the page write timing spec-
ifications. It should also be noted that the data in the enable and disable command sequences
is not written to the device and the memory addresses used in the sequence may be written
with data in either a byte or page write operation.
After setting SDP, any attempt to write to the device without the three 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 polling operations.
4.6.2
4.7
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 7FC0H to 7FFFH the additional bytes
may be written to or read from in the same manner as the regular memory array.
4.8
Optional Chip Erase Mode
The entire device can be erased using a 6-byte software code. Please see “Software Chip
Erase” application note for details.
4
AT28HC256
0007J–PEEPR–04/05
AT28HC256
5. DC and AC Operating Range
AT28HC256-70
Com.
Operating
Temperature (Case)
V
CC
Power Supply
Ind.
Mil.
5V
±
10%
0°C - 70°C
-40°C - 85°C
AT28HC256-90
0°C - 70°C
-40°C - 85°C
-55°C - 125°C
5V
±
10%
AT28HC256-12
0°C - 70°C
-40°C - 85°C
-55°C - 125°C
5V
±
10%
6. Operating Modes
Mode
Read
Write
(2)
Standby/Write Inhibit
Write Inhibit
Write Inhibit
Output Disable
Chip Erase
Notes: 1. X can be V
IL
or V
IH
.
2. Refer to AC programming waveforms.
3. V
H
= 12.0V ± 0.5V.
CE
V
IL
V
IL
V
IH
X
X
X
V
IL
OE
V
IL
V
IH
X
(1)
X
V
IL
V
IH
V
H(3)
WE
V
IH
V
IL
X
V
IH
X
X
V
IL
High Z
High Z
I/O
D
OUT
D
IN
High Z
7. Absolute Maximum Ratings*
Temperature under Bias ................................ -55°C to +125°C
Storage Temperature ..................................... -65°C to +150°C
All Input Voltages
(including NC Pins)
with Respect to Ground ...................................-0.6V to +6.25V
All Output Voltages
with Respect to Ground .............................-0.6V to V
CC
+ 0.6V
Voltage on OE and A9
with Respect to Ground ...................................-0.6V to +13.5V
*NOTICE:
Stresses beyond those listed under “Absolute
Maximum Ratings” may cause permanent dam-
age to the device. This is a stress rating only and
functional operation of the device at these or any
other conditions beyond those indicated in the
operational sections of this specification is not
implied. Exposure to absolute maximum rating
conditions for extended periods may affect
device reliability
8. DC Characteristics
Symbol
I
LI
I
LO
I
SB1
I
SB2
I
CC
V
IL
V
IH
V
OL
V
OH
Parameter
Input Load Current
Output Leakage Current
V
CC
Standby Current TTL
V
CC
Standby Current CMOS
V
CC
Active Current
Input Low Voltage
Input High Voltage
Output Low Voltage
Output High Voltage
I
OL
= 6.0 mA
I
OH
= -4 mA
2.4
2.0
0.45
Condition
V
IN
= 0V to V
CC
+ 1V
V
I/O
= 0V to V
CC
CE = 2.0V to V
CC
CE = V
CC
- 0.3V to V
CC
f = 5 MHz; I
OUT
= 0 mA
AT28HC256-90, -12
AT28HC256-70
AT28HC256-90, -12
Min
Max
10
10
3
60
300
80
0.8
Units
µA
µA
mA
mA
µA
mA
V
V
V
V
5
0007J–PEEPR–04/05
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