AS29F400
®
Preliminary information
Functional description
The AS29F400 is a 4 megabit, 5 volt only Flash memory organized as 512K bytes of 8 bits each or 256K words of 16 bits each. For flexible
erase and program capability, the 4 megabits of data is divided into 11 sectors: one 16K byte, two 8K byte, one 32K byte, and seven 64K
byte. The ×8 data appears on DQ0–DQ7; the ×16 data appears on DQ0–DQ15. The AS29F400 is offered in JEDEC standard 44-pin SO and
48-pin TSOP packages. This device is designed to be programmed and erased in-system with a single 5.0V V
CC
supply. The device can also
be reprogrammed in standard EPROM programmers.
The AS29F400 offers access times of 55/70/90/120/150 ns, allowing 0-wait state operation of high speed microprocessors. To eliminate
bus contention the device has separate chip enable (CE), write enable (WE), and output enable (OE) controls. Word mode (×16 output) is
selected by BYTE = High and Byte mode (×8 output) is selected by BYTE = Low.
The AS29F400 is fully compatible with the JEDEC single power supply Flash standard. Write commands to the command register using
standard microprocessor write timings. An internal state-machine uses register contents to control the erase and programming circuitry.
Write cycles also internally latch addresses and data needed for the programming and erase operations. Read data from the device in the
same manner as other Flash or EPROM devices. Use the program command sequence to invoke the automated on-chip programming
algorithm that automatically times the program pulse widths and verifies proper cell margin. Use the erase command sequence to invoke the
automated on-chip erase algorithm that preprograms the sector if it is not already programmed before executing the erase operation, times
the erase pulse widths, and verifies proper cell margin.
Boot sector architecture enables the device to boot from either the top (AS29F400T) or bottom (AS29F400B) sector. Sector erase
architecture allows specified sectors of memory to be erased and reprogrammed without altering data in other sectors. A sector typically
erases and verifies within 1.0 seconds. Hardware sector protection disables both program and erase operations in all or any combination of
the eleven sectors. The device provides true background erase with Erase Suspend, which puts erase operations on hold to either read data
from or program data to a sector that is not being erased. The chip erase command will automatically erase all unprotected sectors.
A factory shipped AS29F400 is fully erased (all bits = 1). The programming operation sets bits to 0. Data is programmed into the array one
byte/word at a time in any sequence and across sector boundaries. A sector must be erased to change bits from 0 to 1. Erase returns all
bytes/words in a sector to the erased state (all bits = 1). Each sector is erased individually with no effect on other sectors.
The device features single 5.0V power supply operation for read, write, and erase functions. Internally generated and regulated voltages are
provided for the program and erase operations. A low V
CC
detector automatically inhibits write operations during power transtitions. The
RY/BY pin, DATA polling of DQ7, or toggle bit (DQ6) may be used to detect end of program or erase operations. The device automatically
resets to the read mode after program/erase operations are completed. DQ2 indicates which sectors are being erased.
The AS29F400 resists accidental erasure or spurious programming signals resulting from power transitions. Control register architecture
permits alteration of memory contents only after successful completion of specific command sequences. During power up, the device is set
to read mode with all program/erase commands disabled when V
CC
is less than V
LKO
(lockout voltage). The command registers are not
affected by noise pulses of less than 5 ns on OE, CE, or WE. CE and WE must be logical zero and OE a logical one to initiate write commands.
When the device’s hardware RESET pin is driven low, any program/erase operation in progress will be terminated and the internal state
machine will be reset to read mode. If the RESET pin is tied to the system reset circuitry and a system reset occurs during an automated on-
chip program/erase algorithm, data in address locations being operated on will become corrupted and require rewriting. Resetting the
device enables the system’s microprocessor to read boot-up firmware from the Flash memory.
The AS29F400 uses Fowler-Nordheim tunnelling to electrically erase all bits within a sector simultaneously. Bytes/words are programmed
one at a time using EPROM programming mechanism of hot electron injection.
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ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
