Datasheet 28C256ATC-1, 28C256ASM-4, 28C256ASM-3, 28C256ASM-2, 28C256ASM-1 Datasheet (Turbo IC)

HIGH SPEED CMOS

256K ELECTRICALLY ERASABLE PROGRAMMABLE ROM

32K X 8 BIT EEPROM

ADDRESSES (A0 - A14)

The Addresses are used to select an 8 bits
memory location during a write or read opera­tion.

OUTPUT ENABLE (OE)

The Output Enable input activates the output buff­ers during the read operations.

CHIP ENABLES (CE)

The Chip Enable input must be low to enable all
read/write operation on the device. By setting CE
high, the device is disabled and the power con­sumption is extremely low with the standby cur­rent below 200 µA.

FEATURES:

• 120 ns Access Time

• Automatic Page Write Operation
Internal Control Timer
Internal Data and Address Latches for 64 Bytes

• Fast Write Cycle Times
Byte or Page Write Cycles: 10 ms
Time to Rewrite Complete Memory: 5 sec
T ypical Byte Write Cycle Time: 160 µsec

• Software Data Protection

• Low P ower Dissipation
50 mA Active Current
200 µA CMOS Standby Current

• Direct Microprocessor End of Write Detection
Data Polling

• High Reliability CMOS Technology with Self Redundant

EEPROM Cell

Endurance: 100,000 Cycles
Data Retention: 10 Years

• TTL and CMOS Compatible Inputs and Outputs

• Single 5 V ± 10% P ow er Supply f or Read and

Programming Operations

• JEDEC Approved Byte-Write Pinout

DESCRIPTION:

The Turbo IC 28C256A is a 32K X 8 EEPROM fabricated
with Turbo’s proprietary, high reliability, high performance
CMOS technology . The 256K bits of memory are organized
as 32K by 8 bits. The device offers access time of 120 ns
with power dissipation below 250 mW.

The 28C256A has a 64-bytes page write operation, enabling
the entire memory to be typically written in less than 5.0
seconds. During a write cycle, the address and 1 to 64 b ytes
of data are internally latched, freeing the address and data
bus for other microprocessor operations. The programming
process is automatically controlled by the device using an
internal control timer. Data polling on one or all I/O can be
used to detect the end of a programming cycle. In addition,
the 28C256A includes an user-optional software data write
mode offering additional protection against unwanted (false)
write. The de vice utiliz es an error protected self redundant
cell for extended data retention and endur ance.

WRITE ENABLE (WE)

The Write Enable input initiates the writing of data
into the memory.

DATA INPUT/OUTPUT (I/O0-I/O7)

Data Input/Output pins are used to read data out
of the memory or to write Data into the memory.

PIN DESCRIPTION

4

3

5

2

1

6
7
8
9
10
11
12
13

303132

A8
A9
A11
NC
OE
A10
CE
I/O7
I/O6

A6
A5
A4
A3
A2
A1
A0

NC

I/O0

I/O1

I/O2

GNDNCI/O3

I/O4

I/O5

A12

A7 A14NCVCCWEA13

32 pins PLCC

1
2
3
4
5
6
7
8
9
10
11
12
13
14 15

16

17

18

19

20

21

22

23

24

25

26

27

28A14

A12

A7
A6
A5
A4
A3
A2
A1

A0
I/O0
I/O1
I/O2

GND

VCC
WE
A13
A8
A9
A11
OE
A10
CE
I/O7
I/O6
I/O5
I/O4
I/O3

1
2
3
4
5
6
7
8
9
10
11
12
13
14 15

16

17

18

19

20

21

22

23

24

25

26

27

28A14

A12

A7
A6
A5
A4
A3
A2
A1

A0
I/O0
I/O1
I/O2

GND

VCC
WE
A13
A8
A9
A11
OE
A10
CE
I/O7
I/O6
I/O5
I/O4
I/O3

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
I/O7
I/O5
I/O3
I/O2
I/O0
A1

A2

A0

I/O1

GND

I/O4

I/O6

CE

OE

A9

A13

VCC

A12

A6
A4

A3

A5

A7

A14

WE

A8

A11

28 pins PDIP

28 pins SOIC (SOG)

28 pins TSOP

14

29
28
27
26
25
24
23
22

21

20

19

18

17

16

15

Turbo IC, Inc.

28C256A

a.) Software Write Protect Enable

A sequence of three dummy data writes to the memory will activate
internal EEPROM fuses during the first page write cycle. These EE­PROM fuses will reject any write attempts of new pages of data
unless the three dummy data writes are repeated at the beginning of
any page writes. The timing f or the dummy data and addresses m ust
be the same as for a normal write operation. A violation of the three
steps write protect sequence in data or address timing and content
will abort the procedure and reset the device to the starting point
condition.

Note: After the three dummy data writes, at least one page load/
write cycle must be performed. If no additional page data is added
to the three dummy data writes, the software write protect will
not be enabled until the next write, which will not be protected.

T able 1 sho ws the required procedure for enab ling the software write
protect:

Step Mode Address A14-A0 Data I/O 7-0
1 Page Write 5555 Hex AA Hex
2 Page Write 2AAA Hex 55 Hex
3 Page Write 5555 Hex A0 Hex
4-67 Page Write Address Data

b.) Software Write Protect Disable

The software algorithm of 28C256A includes a six steps sequence
of dummy data writing to disable the software write protect feature
described in a.). The six steps write sequence shown in Table 2 must
be performed at the beginning of a page write cycle. A violation of
the six steps write sequence in data or address timing and content
will abort the procedure and reset the chip to the starting point con­dition. After a page write cycle including the six steps write sequence
has been performed, the 28C256A does not require the use of three
dummy data writes described in a.) for the following page write cycle.
The device is at the software write protect disabled state.

Note: After the six dummy data writes, at least one page load/
write cycle must be performed. If no additional page data is added
to the six dummy data writes, the software write pr otect disable
will not be activated. Table 2 shows the required procedure for dis-

abling the software write protect:
Step Mode Address A14-A0 Data I/O 7-0

1 Page Write 5555 Hex AA Hex
2 Page Write 2AAA Hex 55 Hex
3 Page Write 5555 Hex 80 Hex
4 Page Write 5555 Hex AA Hex
5 Page Write 2AAA Hex 55 Hex
6 Page Write 5555 Hex 20 Hex
7-70 Page Write Address Data

c.) Software Chip Clear

The software algorithm of 28C256A includes a sequence of six steps
dummy data writing to perform a chip clear operation. Table 3 shows
the six steps write sequence to perform the software chip clear op­eration:

Step Mode Address A14-A0 Data I/O 7-0
1 Page Write 5555 Hex AA Hex
2 Page Write 2AAA Hex 55 Hex
3 Page Write 5555 Hex 80 Hex
4 Page Write 5555 Hex AA Hex
5 Page Write 2AAA Hex 55 Hex
6 Page Write 5555 Hex 10 Hex

At the end of the six steps write sequence shown in Table 3, the
device automatically activates its internal timer to control the chip

DEVICE OPERA TION

READ:

The 28C256A is accessed like a static RAM. Read operations are initi­ated by both CE and OE going low and terminated by either CE or OE
returning high. The outputs are at the high impedance state whenever
CE or OE returns high. The two line control architecture gives designers
flexibility in preventing bus contention.

WRITE:

A write cycle is initiated when CE and WE are low and OE is high. The
address is latched internally on the falling edge of CE or WE whichever
occurs last. The data is latched b y the rising edge of CE or WE whiche ver
occurs first. Once a byte write cycle has been started, the inter nal timer
automatically generates the write sequence to the completion of the write
operation.

P AGE WRITE OPERATION:

The page write operation of 28C256A allows one to 64 bytes of data to
be serially loaded into the device and then simultaneously written into
memory during the internally generated wr ite cycle. After the first byte
has been loaded, successive bytes of data may be loaded until the full
page of 64 bytes is loaded. Each new byte to be written must be loaded
within 200 µs of the previously loaded byte. The page address defined by
the addresses A6-A14 is latched by the first CE or WE f alling edge which
initiates a writing cycle and they will stay latched until the completion of
the page write. Any changes in the page addresses during the load-write
cycle will not affect the initially latched page addresses. Addresses A0 ­A5 are used to define which bytes will be loaded and written within the 64
bytes page. The bytes may be loaded in any order that is convenient to
the user. The content of a loaded byte may be altered at any time during
the loading cycle if the maximum allowed byte-load time (200 µs) is not
exceeded. Only loaded bytes within the page will be written; no rewriting
will occur to the non-selected bytes in the page.

DATA POLLING:

The 28C256A features DATA POLLING to indicate the completion of a
write cycle to the host system. During a byte or page write cycle, an
attempted read of the last byte loaded into the page will result in the
complement of the loaded byte on all outputs I/O0 - I/O7 (i.e. loaded data
01010110, read data 10101001). Data P olling f eature may be used by an
attempted read on one or more outputs (whatever is convenient for the
system developer). Once the write cycle has been completed, true data
is valid on all outputs and the next cycle may be started.

DATA PROTECTION:

The 28C256A has three hardware features to protect the written content
of the memory against inadvertent writes :

a.) Vcc threshold detector: If Vcc is below 2.5 V, the wr ite capa­bilities of the chip is inhibited for whatever input conditions.
b.) Noise protection: A WE, OE, or CE pulse less than 10 ns in
width is not able to initiate a write cycle.
c.) Write inhibit: Holding OE at low, or CE at high, or WE at high
inhibits the write cycle.

SOFTWARE WRITE PROTECTION:

The 28C256A offers a software controlled data write protection feature.
The device is delivered to the user with the software data write protection
DISABLED; i.e. the device will go to the data write operation as long as
Vcc exceeds 2.5 V and CE, WE, and OE inputs are set at write mode
levels. The 28C256A can be automatically protected against an accidental
write operation during power-up or power-down without any external cir­cuitry by enabling the software data write protection features. This f eatures
is enabled after the first write cycle which includes the software algorithm.
After this operation is done, the data write function of the device may be
performed only if every page write cycle is preceded by the software algo­rithm. The device will maintain its software protect feature f or the rest of its
life unless that the software algorithm for disabling the protection is imple­mented.

SOFTWARE ALGORITHM:

The 28C256A has an internal register for the software algorithm which
enables the memory to provide the user with additional features:

Turbo IC, Inc.

28C256A

erase cycle; typically takes 20 msec. After a software chip clear op­eration has been completed, all 256K bit locations of memory show
high level at read operation mode.

d.) Software Autoclear Disable Mode

This software algorithm disables the internal automatic clear before
write cycle. Table 4 shows the six steps needed to perf orm the auto­clear disable mode:

Step Mode Address A14-A0 Data I/O 7-0
1 Page Write 5555 Hex AA Hex
2 Page Write 2AAA Hex 55 Hex
3 Page Write 5555 Hex 80 Hex
4 Page Write 5555 Hex AA Hex
5 Page Write 2AAA Hex 55 Hex
6 Page Write 5555 Hex 40 Hex
7-70 Page Write Address Data

Page write operation using the software autoclear disable mode will
reduce programming time to typically 5 msec. The page write using
software autoclear disable mode is usually used after a chip clear or
a software chip clear operation. At the end of the six steps sequence,
the autoclear before write is disabled and will stay that wa y unless a
power-down occurs or the software autoclear enable procedure is
initiated.

e.) Software Autoclear Enable Mode

Automatic page clear before page write can be restored to 28C256A
either by Vcc power-down or by software autoclear enable mode.
Table 5 shows the six steps page write procedure needed to enable
software autoclear mode:

Step Mode Address A14-A0 Data I/O 7-0
1 Page Write 5555 Hex AA Hex
2 Page Write 2AAA Hex 55 Hex
3 Page Write 5555 Hex 80 Hex
4 Page Write 5555 Hex AA Hex
5 Page Write 2AAA Hex 55 Hex
6 Page Write 5555 Hex 50 Hex
7-70 Page Write Address Data

Symbol Parameter Condition Min Max Units

Icc Active Vcc CE=OE=Vil; All I/O 50 (C) mA

Current Open, Min Read or 70 (I) mA

Write Cycle Time 90 (M) mA

Isb1 CMOS CE=Vcc-0.3 V to 200 (C) µA

Standby Vcc+1 V 300 (I&M) µA
Current

Isb2 TTL Standby CE=Vih, OE=Vil, 3 mA

Current All I/O Open, Other

Inputs=Vcc Max
Vin=Vcc Max

Iil Input 1 µA

Leakage
Current

Iol Output 10 µA

Leakage
Current

Vil Input Low -0.1 -0.8 V

Voltage

Vih Input High 2 Vcc+0.3 V

Voltage

Vo l Output Low Iol=2.1 mA 0.45 V

Voltage

Voh Output High Ioh=-0.45 mA 2.4 V

Voltage

D.C. CHARACTERISTICS

(C) = COMMERCIAL
(I) = INDUSTRIAL
(M) = MILITARY

Turbo IC, Inc.

28C256A

ABSOLUTE MAXIMUM STRESS RANGES *

TEMPERATURE

Storage: -65° C to 150° C
Under Bias: -55° C to 125° C

ALL INPUT OR OUTPUT VOLTAGES

with respect to Vss +6 V to -0.3 V

“Absolute Maximum Ratings” ma y cause perma­nent damage to the device. This is a stress rating
only and functional operation of the device at
these or any other conditions above those indi­cated in the operation section of this specifica­tion is not implied. Exposure to absolute maxi­mum rating conditions for extended periods may
affect device reliability.

RECOMMENDED OPERATING CONDITIONS
Temperature Range: Commercial: 0° C to 70° C

Industrial: -40° C to 85° C
Military: -55° C to 125° C

Vcc Supply Voltage:5 V ± 10%

Endurance: 100,000 Cycles/Byte (Typical)
Data Retention: 10 Years

A.C. CHARACTERISTICS - READ OPERATION

28C256A-1 28C256A-2 28C256A-3 28C256A-4

Symbol Parameters Min Max Min Max Min Max Min MaxUnit
tacc Address to 120 150 200 250 ns

Output Delay

tce CE to Output 120 150 200 250 ns

Delay
toe OE to Output 70 90 110 150 ns
tdf OE to Output 0 40 0 60 0 90 0 90 ns

In High Z
toh Output Hold 0000ns

from Address

Changes, Chip

Enable or

Output Enable

Whichever

Occurs First

A.C. Read Wave Forms

A.C. TEST CONDITIONS

Output Load : 1 TTL Load and Cl=100 pF
Input Rise and Fall Times : < 10 ns
Input Pulse Level : 0 V to 3 V
Timing Measurement Reference Level : 1.5 V

tacc

ADDRESS VALIDADDRESS

CE

OE

OUTPUT HIGH-Z

toe

tce

tdf

toh

OUTPUT VALID

HIGH-Z

TURBO IC PRODUCTS AND DOCUMENTS

1. All documents are subject to change without notice. Please contact Turbo IC for the latest
revision of documents.

2. Turbo IC does not assume any responsibility for any damage to the user that may result from
accidents or operation under abnormal conditions.

3. Turbo IC does not assume any responsibility for the use of any circuitry other than what
embodied in a Turbo IC product. No other circuits, patents, licenses are implied.

4. Turbo IC products are not authorized for use in life support systems or other critical systems
where component failure may endanger life. System designers should design with error
detection and correction, redundancy and back-up features.

A.C. WRITE CHARACTERISTICS

Symbol Parameter Min Max Units
tas Address Set-up Time 20 ns
tah Address Hold Time 100 ns
tcs Write Set-up Time 0 ns
tch Write Hold Time 0 ns
tcw CE Pulse Width 150 ns
twp WE Pulse Width 150 ns
toes OE Set-up Time 20 ns
toeh OE Hold Time 20 ns
tds Data Set-up Time 50 ns
tdh Data Hold Time 0 ns
tdh Data Hold (28C256A-4 ONLY) 10 ns
tblc Byte Load Cycle 0.2 200 µs
tlp Last Byte Loaded to Data

Polling Output 500 µ s
twc Write Cycle Time 10 m s
twc Write Cycle Time (IND & MIL) 15 ms

Part Numbers & Order Inf ormation

28C256APC-2

Speed

-1 120 ns

-2 150 ns

-3 200 ns

-4 250 ns

Temperature
C -Commercial
I -Industrial
M -Military

Package
J -PLCC

P -PDIP

S -SOIC
T -TSOP

Turbo IC, Inc. 2365 Paragon Drive, Suite I, San Jose, CA 95131 Phone: [phone] Fax: [phone]

See us at www.turbo-ic.com

32K x 8
EEPROM

Page Mode Write Wave Form

PAGE MODE WRITE CHARACTERISTICS

Symbol Parameter Min Max Unit

twc Write Cycle Time 10 ms
tas Address Set-up Time 20 n s
tah Address Hold Time 100 ns
tds Data Set-up Time 50 ns
tdh Data Hold Time 0 ns
twp Write Pulse Width 150 ns
tblc Byte Load Cycle Time 0.2 200 µ s

Chip Clear Wave Form

The content of the 28C256A may be altered to HIGH by the use of the
Chip Clear operation. By setting CE to low, OE to 12 volts, and WE to
low, the entire memory can be cleared (written HIGH) within 20 ms. The
Chip Clear operation is a latch operation mode. After the Chip Clear
starts, the internal chip timer takes over and completes the clear with­out CE, OE and WE being held active.

A.C. Write Characteristics CE-Controlled

A.C. Write Characteristics WE-Controlled

OE

ADDRESS

CE

WE

DATA

toes

tas

tcs tah

toeh

tch

tcw

tds

tblc

twc

tdh

HIGH-Z

DATA VALID

HIGH-Z

VALID

OE

ADDRESS

CE

WE

DATA

toes

tas

tcs tah

toeh

tch

twp

tds

tblc

twc

tdh

HIGH-Z

DATA VALID

HIGH-Z

VALID

OE

CE

WE

A0-A5

DATA

twp

tblc

tah

tas

tds

tdh

BYTE-0

BYTE-1

BYTE-2

AD-VALID

AD-VALID

AD-VALID

OE

CE

WE

ts= 20 ns
tp= 200 ns
th= 20 ns
VH=12.0 V±0.5V

tp

th

VH

VIH

VIH

VIL

VIH

VIL

ts

Turbo IC, Inc.

28C256A

Rev . 4.0 - 10/28/01