FINAL
Am28F256A
256 Kilobit (32 K x 8-Bit)
CMOS 12.0 Volt, Bulk Erase Flash Memory with Embedded Algorithms
DISTINCTIVE CHARACTERISTICS
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High performance
— Access times as fast as 70 ns
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CMOS low power consumption
— 30 mA maximum active current
— 100 µA maximum standby current
— No data retention power consumption
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Compatible with JEDEC-standard byte-wide
32-Pin EPROM pinouts
— 32-pin PDIP
— 32-pin PLCC
— 32-pin TSOP
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100,000 write/erase cycles minimum
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Write and erase voltage 12.0 V
±5%
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Latch-up protected to 100 mA from –1 V to
V
CC
+1 V
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Embedded Erase Electrical Bulk Chip-Erase
— 1.5 seconds typical chip-erase including
pre-programming
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Embedded Program
— 14 µs typical byte-program including time-out
— 0.5 second typical chip program
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Command register architecture for
microprocessor/microcontroller compatible
write interface
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On-chip address and data latches
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Advanced CMOS flash memory technology
— Low cost single transistor memory cell
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Embedded algorithms for completely
self-timed write/erase operations
GENERAL DESCRIPTION
The Am28F256A is a 256 K Flash memory organized
as 32 Kbytes of 8 bits each. AMD’s Flash memories
offer the most cost-effective and reliable read/write
non- volatile random access memory. The Am28F256A
is packaged in 32-pin PDIP, PLCC, and TSOP versions.
It is designed to be reprogrammed and erased in-sys-
tem or in standard EPROM programmers. The
Am28F256A is erased when shipped from the factory.
The standard Am28F256A offers access times as fast
as 70 ns, allowing operation of high-speed micropro-
cessors without wait states. To eliminate bus conten-
tion, the Am28F256A has separate chip enable (CE#)
and output enable (OE#) controls.
AMD’s Flash memories augment EPROM functionality
with in-circuit electrical erasure and programming. The
Am28F256A uses a command register to manage this
functionality, while maintaining a standard JEDEC
Flash Standard 32-pin pinout. The command register
allows for 100% TTL level control inputs and fixed
power supply levels during erase and programming.
AMD’s Flash technology reliably stores memory con-
tents even after 100,000 erase and program cycles.
The AMD cell is designed to optimize the erase and
Publication#
18879
Rev:
C
Amendment/+2
Issue Date:
May 1998
programming mechanisms. In addition, the combina-
tion of advanced tunnel oxide processing and low inter-
nal electr ic fields for erase a nd programmi ng
operations produces reliable cycling. The Am28F256A
uses a 12.0V± 5% V
PP
high voltage input to perform
the erase and programming functions.
The highest degree of latch-up protection is achieved
with AMD’s proprietary non-epi process. Latch-up pro-
tection is provided for stresses up to 100 milliamps on
address and data pins from –1 V to V
CC
+1 V.
Embedded Program
The Am28F256A is byte programmable using the
Embedded Programming algorithm. The Embedded
Programming algorithm does not require the system to
time-out or verify the data programmed. The typical
room temperature programming time of the
Am28F256A is one half second.
Embedded Erase
The entire chip is bulk erased using the Embedded
Erase algorithm. The Embedded Erase algorithm
automatically programs the entire array prior to electrical
erase. The timing and verification of electrical erase are
controlled internal to the device. Typical erasure at room
temperature is accomplished in 1.5 seconds, including
preprogramming.
AMD’s Am28F256A is entirely pin and software com-
patible with AMD’s Am28F020A, Am28F256A and
Am28F512A Flash memories.
Comparing Embedded Algorithms with Flasherase and Flashrite Algorithms
Am28F256A with
Embedded Algorithms
Embedded
Programming
Algorithm vs.
Flashrite
Programming
Algorithm
AMD’s Embedded Programming algorithm
requires the user to only write a program
set-up command and a program command
(program data and address). The device
automatically times the programming
pulse width, verifies the programming, and
counts the number of sequences. A status
bit, Data
#
Polling, provides the user with
the programming operation status.
Am28F256 using AMD Flashrite
and Flasherase Algorithms
The Flashrite Programming algorithm requires the
user to write a program set-up command, a program
command, (program data and address), and a
program verify command, followed by a read and
compare operation. The user is required to time the
programming pulse width in order to issue the
program verify command. An integrated stop timer
prevents any possibility of overprogramming.
Upon completion of this sequence, the data is read
back from the device and compared by the user with
the data intended to be written; if there is not a
match, the sequence is repeated until there is a
match or the sequence has been repeated 25 times.
The Flasherase Erase algorithm requires the device
to be completely programmed prior to executing an
erase command.
To invoke the erase operation, the user writes an
erase set-up command, an erase command, and an
erase verify command. The user is required to time
the erase pulse width in order to issue the erase
verify command. An integrated stop timer prevents
any possibility of overerasure.
Upon completion of this sequence, the data is read
back from the device and compared by the user with
erased data. If there is not a match, the sequence is
repeated until there is a match or the sequence has
been repeated 1,000 times.
Embedded Erase
Algorithm vs.
Flasherase Erase
Algorithm
AMD’s Embedded Erase algorithm
requires the user to only write an erase set-
up command and erase command. The
device automatically pre-programs and
verifies the entire array. The device then
automatically times the erase pulse width,
verifies the erase operation, and counts
the number of sequences. A status bit,
Data
#
Polling, provides the user with the
erase operation status.
Commands are written to the command register using
standard microprocessor write timings. Register con-
tents serve as inputs to an internal state-machine which
controls the erase and programming circuitry. During
write cycles, the command register internally latches
address and data needed for the programming and
erase operations. For system design simplification, the
Am28F256A is designed to support either WE# or CE#
controlled writes. During a system write cycle,
addresses are latched on the falling edge of WE# or
CE# whichever occurs last. Data is latched on the rising
edge of WE# or CE# whichever occurs first. To simplify
the following discussion, the WE# pin is used as the
write cycle control pin throughout the rest of this text. All
setup and hold times are with respect to the WE# signal.
AMD’s Flash technology combines years of EPROM
and EEPROM experience to produce the highest levels
of quality, reliability, and cost effectiveness. The
Am28F256A electrically erases all bits simultaneously
using Fowler-Nordheim tunneling. The bytes are
programmed one byte at a time using the EPROM
programming mechanism of hot electron injection.
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Am28F256A
Real-time operating system RTOS
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