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AT29C256 Datasheet(PDF) 3 Page - ATMEL Corporation |
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AT29C256 Datasheet(HTML) 3 Page - ATMEL Corporation |
3 / 17 page 3 AT29C256 0046P–FLASH–10/04 PROGRAM: The device is reprogrammed on a page basis. If a byte of data within a page is to be changed, data for the entire page must be loaded into the device. Any byte that is not loaded during the programming of its page will be indeterminate. Once the bytes of a page are loaded into the device, they are simultaneously programmed during the internal programming period. After the first data byte has been loaded into the device, successive bytes are entered in the same manner. Each new byte to be pro- grammed must have its high-to-low transition on WE (or CE) within 150 µs of the low-to- high transition of WE (or CE) of the preceding byte. If a high-to-low transition is not detected within 150 µs of the last low-to-high transition, the load period will end and the internal programming period will start. A6 to A14 specify the page address. The page address must be valid during each high-to-low transition of WE (or CE). A0 to A5 specify the byte address within the page. The bytes may be loaded in any order; sequential loading is not required. Once a programming operation has been initiated, and for the duration of t WC, a read operation will effectively be a polling operation. SOFTWARE DATA PROTECTION: A software controlled data protection feature is available on the AT29C256. Once the software protection is enabled a software algo- rithm 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 page program timing specifications. Once set, the software data protection feature remains active unless its disable command is issued. Power transitions will not reset the software data protection feature, however the soft- ware feature will guard against inadvertent 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 three-byte command sequence will start the internal write timers. No data will be written to the device; how- ever, for the duration of tWC, a read operation will effectively be a polling operation. After the software data protection’s three-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 (respec- tively) 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 64 bytes of data must be loaded into each sector by the same procedure as outlined in the program section under device operation. HARDWARE DATA PROTECTION: Hardware features protect against inadvertent programs to the AT29C256 in the following ways: (a) VCC sense – if VCC is below 3.8V (typical), the program function is inhibited; (b) VCC power on delay – once VCC has reached the VCC sense level, the device will automatically time out 5 ms (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. |
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