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0383J–FLASH–9/08

AT29BV040A

3.

Block Diagram

4.

Device Operation

4.1

Read

The AT29BV040A 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 con-

trol gives designers flexibility in preventing bus contention.

4.2

Software Data Protection Programming

The AT29BV040 has 2048 individual sectors, each 256 bytes. Using the software data protec-

tion feature, byte loads are used to enter the 256 bytes of a sector to be programmed. The

AT29BV040A can only be programmed or reprogrammed using the software data protection

feature. The device is programmed on a sector basis. If a byte of data within the sector is to be

changed, data for the entire 256-byte sector must be loaded into the device. The AT29BV040A

automatically does a sector erase prior to loading the data into the sector. An erase command is

not required.

Software data protection protects the device from inadvertent programming. A series of three

program commands to specific addresses with specific data must be presented to the device

before programming may occur. The same three program commands must begin each program

operation. All software program commands must obey the sector program timing specifications.

Power transitions will not reset the software data protection feature, however the software fea-

ture will guard against inadvertent program cycles during power transitions.

Any attempt to write to the device without the 3-byte command sequence will start the internal

write timers. No data will be written to the device; however, for the duration of t

tion will effectively be a polling operation.

After the software data protection’s 3-byte command code is given, a byte load is performed 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, whichever occurs last. The data is latched by

the first rising edge of CE or WE.

The 256 bytes of data must be loaded into each sector. Any byte that is not loaded during the

programming of its sector will be indeterminate. Once the bytes of a sector are loaded into the

device, they are simultaneously programmed during the internal programming period. After the