4

AT49BV/LV2048A

1914D–FLASH–03/02

SECTOR ERASE: As an alternative to a full chip erase, the device is organized into four sec-

tors that can be individually erased. There are two 4K word parameter block sections, one

boot block, and the main memory array block. 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 auto-

matically time to completion. Whenever the main memory block is erased and reprogrammed,

the two parameter blocks should be erased and reprogrammed before the main memory block

is erased again. Whenever a parameter block is erased and reprogrammed, the other param-

eter block should be erased and reprogrammed before the first parameter block is erased

again. Whenever the boot block is erased and reprogrammed, the main memory block and the

parameter blocks should be erased and reprogrammed before the boot block is erased again.

BYTE/WORD PROGRAMMING: Once a memory block is erased, it is programmed (to a logic

“0”) on a byte-by-byte or word-by-word basis. Programming is accomplished via the internal

device command register and is a four-bus cycle operation. The device will automatically gen-

erate 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”; only erase

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 8K words. 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 activated; the boot block’s usage as

a write-protected region is optional to the user. The address range of the boot block is 00000H

to 01FFFH.

Once the feature is enabled, the data in the boot block can no longer be erased or pro-

grammed when input levels of 5.5V or less are used. Data in the main memory block can still

be changed through the regular programming method. To activate the lockout feature, a series

of six program commands to specific addresses with specific data must be performed. Please

refer to the Command Definitions table.

BOOT BLOCK LOCKOUT DETECTION: A software method is available to determine if pro-

gramming of the boot block section is locked out. When the device is in the software product

identification mode (see Software Product Identification Entry and Exit sections) a read from

the following address location will show if programming the boot block is locked out – 00002H.

If the data on I/O0 is low, the boot block can be programmed; if the data on I/O0 is high, the

program lockout feature has been enabled and the block cannot be programmed. The soft-

ware product identification exit code should be used to return to standard operation.

BOOT BLOCK PROGRAMMING LOCKOUT OVERRIDE: The user can override the boot

block programming lockout by taking the RESET pinto12volts during theentirechiperase,

sector erase or word programming operation. When the RESET pin is brought back to TTL

levels the boot block programming lockout feature is again active.