4

3353F–FLASH–3/05

AT49BV002A(N)(T)

4.3

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. 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” on

page 5). The RESET feature is not available on the AT49BV002AN(T).

4.4

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

erased.

4.4.1

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 - 4, 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.

4.4.2

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 four main memory blocks. The 8K-

byte parameter block sections and the four 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 and 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.

4.5

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 7). The

device will automatically generate the required internal program pulses.