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AT49F040-12JI Datasheet(PDF) 2 Page - ATMEL Corporation |
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AT49F040-12JI Datasheet(HTML) 2 Page - ATMEL Corporation |
2 / 10 page Device Operation READ: The AT49F040 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 control gives designers flexibility in preventing bus contention. ERASURE: Before a byte can be reprogrammed, the 512K bytes memory array (or 496K bytes if the boot block featured is used) must be erased. The erased state of the memory bits is a logical “1". The entire device can be erased at one time by using a 6-byte software code. The software chip erase code consists of 6-byte load com- mands to specific address locations with a specific data pattern (please refer to the Chip Erase Cycle Waveforms). After the software chip erase has been initiated, the device will internally time the erase operation so that no external clocks are required. The maximum time needed to erase the whole chip is tEC. If the boot block lockout feature has been enabled, the data in the boot sector will not be erased. BYTE PROGRAMMING: Once the memory array is erased, the device is programmed (to a logical “0") on a byte-by-byte basis. Please note that a data ”0" cannot be programmed back to a “1"; only erase operations can con- vert ”0"s to “1"s. Programming is accomplished via the in- ternal device command register and is a 4 bus cycle op- eration (please refer to the Command Definitions table). The device will automatically generate the required inter- nal program pulses. The program cycle has addresses latched on the falling edge of WE or CE, whichever occurs last, and the data latched on the rising edge of WE or CE, whichever occurs first. Programming is completed after the specified tBP cy- (continued) Block Diagram The optional 16K bytes boot block section includes a re- programming write lock out feature to provide data integ- rity. The boot sector is designed to contain user secure code, and when the feature is enabled, the boot sector is permanently protected from being reprogrammed. Description (Continued) cle time. The DATA polling feature may also be used to indicate the end of a program cycle. BOOT BLOCK PROGRAMMING LOCKOUT: The de- vice 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 16K bytes. This block, referred to as the boot block, can contain secure code that is used to bring up the system. Enabling the lockout fea- ture 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 03FFFH. Once the feature is enabled, the data in the boot block can no longer be erased or programmed. 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 programming of the boot block section is locked out. When the device is in the software product identification mode (see Software Prod- uct Identification Entry and Exit sections) a read from ad- dress location 00002H will show if programming the boot block is locked out. 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 activated and the block cannot be programmed. The software product identifica- tion code should be used to return to standard operation. 4-210 AT49F040 |
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