The AT49F040B is a 5-volt-only in-system reprogrammable Flash Memory. Its 4 megabits of memory is organized as 524,288 words by 8 bits. Manufactured with Atmel's advanced nonvolatile CMOS technology, the device offers access times to 55 ns with power dissipation of just 110 mW over the commercial temperature range. When the device is deselected, the CMOS standby current is less than 25 A. To allow for simple in-system reprogrammability, the AT49F040B does not require high input voltages for programming. Five-volt-only commands determine the read and programming operation of the device. Reading data out of the device is similar to reading from an EPROM; it has standard CE, OE, and WE inputs to avoid bus contention. Reprogramming the AT49F040B is performed by erasing a sector of data and then programming on a byte by byte basis. The byte programming time is a fast 12 s. The end of a program or erase cycle can be optionally detected by the DATA polling or toggle bit feature. Once the end of a byte program cycle has been detected, a new access for a read or program can begin. The typical number of program and erase cycles is in excess of 100,000 cycles. The device is erased by executing a chip erase or a sector erase command sequence; the device internally controls the erase operations. The memory array of the AT49F040B is organized into two 8K byte parameter sectors, eight main memory sectors, and one boot sector. The device has the capability to protect the data in the boot sector; this feature is enabled by a command sequence. The 16K-byte boot sector includes a reprogramming lock out feature to provide data integrity. 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.