AT49BV/LV001(N)(T)
3
Device Operation
READ:
The AT49BV/LV 001(N)(T) is ac cessed like a n
EPROM. When CE
and OE are low and WE is high, th e
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 con tr ol gi ves des ign er s fl ex ibi lity in pr eventing bus contention.
COMMAND SEQUENCES:
When the device is firs t 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.
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 locations 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 application s. When RE SET
is at a logic high level, the
device is in its standa rd oper at ing mod e. A low l evel on th e
RESET
input halts the prese nt device oper ation 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 op eration wi ll have to be r epeated af ter
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 ap plying a 12V ± 0 .5V in put si gnal t o the
RESET
pin, the boot block array can be reprogrammed
even if the boot block lock out feature has be en enabled
(see Boot Bloc k Prog rammi ng Locko ut Over ride s ection) .
The RESET feature is not available on the
AT49BV/LV001N(T).
ERASURE:
Before a byte can be reprogram med, the main
memory block or parameter block which contains the byte
must be erased. The erased state of th e memory bits is a
logical “1”. The entir e 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 c hip erase has been i niti ate d, the d evi ce
will internally time the eras e operation so that no e xternal
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, M ain Me mory B lock 1, a nd Mai n Memory 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 reprogrammed. The two main memory sections are designed to
be used as alternative memory sectors. That is, whenever
one of the blocks has bee n er as ed and repr og ra mme d, th e
other block should be erased and rep rogrammed be fore
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 ris ing edge of WE
. The
sector erase starts after the rising edge of WE
of the sixth
cycle. The erase op eration is in ternally contr olled; it wil l
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 ba sis. Pl ease n ote tha t a data “0” c annot b e
programmed back to a “1”; only erase operations can convert “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 automatical ly gen erate th e re qui red in ter na l
program pulses.
The program cyc le has address es 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 indi-
cate 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 th e
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. Enablin g the l ockou t feature w ill al low 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 activated; the boot block’ s u sage as a wr i te pro tec ted r eg io n is
optional to the user. The address range of the boot block is
00000 to 03FFF for the AT49BV/LV001(N) while the