AT49F002(N)(T)
3
Device Operation
READ: The AT49F002(N)(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 is
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 conten-
tion.
COMMAND SEQUENCES: When the device is first pow-
ered 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.
The command sequences are written by applying a low
pulse on the WE
or CE input with CE or WE low (respec-
tively) 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 loca-
tions used in the command sequences are not affected by
entering the command sequences.
RESET: A RESET
input pin is provided to ease some sys-
tem 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. If the
RESET
pin makes a high to low transition during a program
or erase operation, the operation may not be successfully
completed and the operation will have to be repeated after
a high level is applied to the RESET
pin. 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. By applying a 12V
± 0.5V input signal to the
RESET
pin, the boot block array can be reprogrammed
even if the boot block lockout feature has been enabled
(see Boot Block Programming Lockout Override section).
The RESET feature is not available for the AT49F002N(T).
ERASURE: Before a byte can be reprogrammed, the main
memory block or parameter block which contains the byte
must be erased. The erased state of the memory bits is a
logical “1”. The entire device can be erased at one time by
using a 6-byte software code. The software chip erase
code consists of 6-byte load commands to specific address
locations with a specific data pattern (please refer to the
Chip Erase Cycle Waveforms).
After the software chip erase has been initiated, the device
will internally time the erase operation so that no external
clocks are required. The maximum time needed to erase
the whole chip is t
EC
. If the boot block lockout feature has
been enabled, the data in the boot sector will not be
erased.
CHIP ERASE: If the boot block lockout has been enabled,
the Chip Erase function will erase Parameter Block 1,
Parameter Block 2, Main Memory Block 1, and Main Mem-
ory Block 2 but not the boot block. If the Boot Block Lockout
has not been enabled, the Chip Erase function will erase
the entire chip. After the full chip erase the device will
return back to read mode. Any command during chip erase
will be ignored.
SECTOR ERASE: As an alternative to a full chip erase, the
device is organized into sectors that can be individually
erased. There are two 8K-byte parameter block sections
and two main memory blocks. The 8K-byte parameter
block sections can be independently erased and repro-
grammed. The two main memory sections are designed to
be used as alternative memory sectors. That is, whenever
one of the blocks has been erased and reprogrammed, the
other block should be erased and reprogrammed before
the first block is again 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 at 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.
BYTE PROGRAMMING: Once the memory array is
erased, the device is programmed (to a logical “0”) on a
byte-by-byte basis. Please note that a data “0” cannot be
programmed back to a “1”; only erase operations can con-
vert “0”s to “1”s. Programming is accomplished via the
internal device command register and is a 4 bus cycle
operation (please refer to the Command Definitions table).
The device will automatically generate the required internal
program pulses.
The program cycle has addresses latched on the falling
edge of WE
or CE, whichever occurs last, and the data
latched on the rising edge of WE
or CE, whichever occurs
first. Programming is completed after the specified t
BP
cycle
time. The DATA
polling feature may also be used to indicate
the end of a program cycle.
BOOT BLOCK PROGRAMMING LOCKOUT: The device
has one designated block that has a programming lockout
feature. This feature prevents programming of data in the
designated block once the feature has been enabled. The
size of the block is 16K bytes. This block, referred to as the
boot block, can contain secure code that is used to bring up
the system. Enabling the lockout feature will allow the boot
code to stay in the device while data in the rest of the
device is updated. This feature does not have to be acti-
vated; the boot block’s usage as a write protected region is
optional to the user. The address range of the boot block is
00000 to 03FFF for the AT49F002(N) while the address
