5
AT49BV1604A(T)/1614A(T)
1411F–FLASH–03/02
Device
Operation
READ: The AT49BV/LV16X4A(T) is accessed like an EPROM. When CE and OE are low and
WE
is high, the data stored at the memory location determined by the address pins are
asserted on the outputs. The outputs are put in the high-impedance state whenever CE
or OE
is high. This dual-line control gives designers flexibility in preventing bus contention.
COMMAND SEQUENCES: When the device is first powered on it will be reset to the read or
standby mode, depending upon the state of the control line inputs. In order to perform other
device functions, a series of command sequences are entered into the device. The command
sequences are shown in the Command Definitions table (I/O8 - I/O15 are don’t care inputs for
the command codes). The command sequences are written by applying a low pulse on the
WE
or CE input with CE or WE low (respectively) and OE high. 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. Standard microprocessor write timings are used. The address locations used in the
command sequences are not affected by entering the command sequences.
RESET: A RESET
input pin is provided to ease some system applications. When RESET is at
a logic high level, the device is in its standard operating mode. A low level on the RESET
input
halts the present device operation and puts the outputs of the device in a high-impedance
state. When a high level is reasserted on the RESET
pin, the device returns to the read or
standby mode, depending upon the state of the control inputs.
ERASURE: Before a byte/word can be reprogrammed, it must be erased. The erased state of
memory bits is a logical “1”. The entire device can be erased by using the Chip Erase com-
mand or individual sectors can be erased by using the Sector Erase command.
CHIP ERASE: The entire device can be erased at one time by using the six-byte chip erase
software code. After the chip erase has been initiated, the device will internally time the erase
operation so that no external clocks are required. The maximum time to erase the chip is t
EC
.
If the sector lockdown has been enabled, the chip erase will not erase the data in the sector
that has been locked out; it will erase only the unprotected sectors. After the chip erase, the
device will return to the read or standby mode.
SECTOR ERASE: As an alternative to a full chip erase, the device is organized into 39 sec-
tors (SA0 - SA38) that can be individually erased. The Sector Erase command is a six-bus
cycle operation. The sector address is latched on the falling WE
edge of the sixth cycle while
the 30H data input command is latched on the rising edge of WE
. The sector erase starts after
the rising edge of WE
of the sixth cycle. The erase operation is internally controlled; it will
automatically time to completion. The maximum time to erase a section is t
SEC
. When the sec-
tor programming lockdown feature is not enabled, the sector will erase (from the same Sector
Erase command). An attempt to erase a sector that has been protected will result in the oper-
ation terminating in 2 µs.
BYTE/WORD PROGRAMMING: Once a memory block is erased, it is programmed (to a logi-
cal “0”) on a byte-by-byte or on a word-by-word basis. Programming is accomplished via the
internal device command register and is a four-bus cycle operation. The device will automati-
cally generate the required internal program pulses.
Any commands written to the chip during the embedded programming cycle will be ignored. If
a hardware reset happens during programming, the data at the location being programmed
will be corrupted. Please note that a data “0” cannot be programmed back to a “1”;onlyerase
operations can convert “0”sto“1”s. Programming is completed after the specified t
BP
cycle
time. The Data
Polling feature or the Toggle Bit feature may be used to indicate the end of a
program cycle.
VPP PIN: The circuitry of the AT49BV/LV16X4A(T) is designed so that the device can be pro-
grammed or erased from the V
CC
power supply or from the VPP input pin. When V
PP
is less
than or equal to the VCC pin, the device selects the V
CC
supply for programming and erase
