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0456H–FLASH–2/05

AT29C512

4.4

Software Data Protection

A software controlled data protection feature is available on the AT29C512. Once the software

protection is enabled a software algorithm must be issued to the device before a program may

be performed. The software protection feature may be enabled or disabled by the user; when

shipped from Atmel, the software data protection feature is disabled. To enable the software

data protection, a series of three program commands to specific addresses with specific data

must be performed. After the software data protection is enabled the same three program com-

mands must begin each program cycle in order for the programs to occur. All software program

commands must obey the sector program timing specifications. Once set, the software data pro-

tection feature remains active unless its disable command is issued. Power transitions will not

reset the software data protection feature; however, the software feature will guard against inad-

vertent program cycles during power transitions.

Once set, software data protection will remain active unless the disable command sequence is

issued.

After setting SDP, 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

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 128 bytes of data must be loaded into each sector by the

same procedure as outlined in the program section under device operation.

4.5

Hardware Data Protection

Hardware features protect against inadvertent programs to the AT29C512 in the following ways:

(a) V

(typical) before programming; (c) Program inhibit – holding any one of OE low, CE high or WE

high inhibits program cycles; and (d) Noise filter – pulses of less than 15 ns (typical) on the WE

or CE inputs will not initiate a program cycle.

4.6

Product Identification

The product identification mode identifies the device and manufacturer as Atmel. It may be

accessed by hardware or software operation. The hardware operation mode can be used by an

external programmer to identify the correct programming algorithm for the Atmel product. In

addition, users may wish to use the software product identification mode to identify the part (i.e.,

using the device code), and have the system software use the appropriate sector size for pro-

gram operations. In this manner, the user can have a common board design for 256K to 4-

megabit densities and, with each density’s sector size in a memory map, have the system soft-

ware apply the appropriate sector size.

For details, see Operating Modes (for hardware operation) or Software Product Identification.

The manufacturer and device code is the same for both modes.