4
3358C–FLASH–3/05
AT49BV040A
4.2 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 com-
mand sequences are entered into the device. The command sequences are shown in the
“Command Definition Table” on page 6. 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 (except for the sixth cycle of the Sector Erase com-
mand), 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.
4.3 Erasure
Before a byte can be reprogrammed, the main memory blocks or parameter blocks which con-
tains 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 opera-
tion 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.
4.3.1 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 - 8, 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.
4.3.2 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 eight main memory blocks. The
8K-byte parameter block sections and the eight main memory blocks can be independently
erased and reprogrammed. The Sector Erase command is a six bus cycle operation. The sector
address is latched on the rising WE
edge of the sixth cycle while the 30H data input command is
also 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.
4.4 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 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 Definition Table” on page 6). 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.
