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AT29C020-10 Datasheet(PDF) 4 Page - ATMEL Corporation |
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AT29C020-10 Datasheet(HTML) 4 Page - ATMEL Corporation |
4 / 11 page ![]() 4 0291S–FLASH–11/08 AT29C020 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. 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 WC, a read operation will effectively be a polling operation. After the software data protection’s 3-byte command code is given, a sector of data is loaded into the device using the sector program timing specifications. 4.5 Hardware Data Protection Hardware features protect against inadvertent programs to the AT29C020 in the following ways: (a) V CC sense – if VCC is below 3.8V (typical), the program function is inhibited; (b) VCC power on delay – once V CC 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. 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 program 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. 4.7 DATA Polling The AT29C020 features DATA polling to indicate the end of a program cycle. During a program cycle an attempted read of the last byte loaded will result in the complement of the loaded data on I/O7. Once the program cycle has been completed, true data is valid on all outputs and the next cycle may begin. DATA polling may begin at any time during the program cycle. 4.8 Toggle Bit In addition to DATA polling the AT29C020 provides another method for determining the end of a program or erase cycle. During a program or erase operation, successive attempts to read data from the device will result in I/O6 toggling between one and zero. Once the program cycle has completed, I/O6 will stop toggling and valid data will be read. Examining the toggle bit may begin at any time during a program cycle. |
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