Ready/Busy status is indicated using bit 7 of the status register. If bit 7 is a 1, then the device is not busy and is ready to accept the next command. If bit 7 is a 0, then the device is in a busy state. The user can continuously poll bit 7 of the status register by stopping SCK at a low level once bit 7 has been output. The status of bit 7 will continue to be output on the SO pin, and once the device is no longer busy, the state of SO will change from 0 to 1. There are eight operations which can cause the device to be in a busy state: Main Memory Page to Buffer Transfer, Main Memory Page to Buffer Compare, Buffer to Main Memory Page Program with Built-in Erase, Buffer to Main Memory Page Program without Built-in Erase, Page Erase, Block Erase, Main Memory Page Program, and Auto Page Rewrite. The result of the most recent Main Memory Page to Buffer Compare operation is indicated using bit 6 of the status register. If bit 6 is a 0, then the data in the main memory page matches the data in the buffer. If bit 6 is a 1, then at least one bit of the data in the main memory page does not match the data in the buffer. The device density is indicated using bits 5, 4, 3 and 2 of the status register. For the AT45DB041B, the four bits are 0, 1, 1 and 1. The decimal value of these four binary bits does not equate to the device density; the four bits represent a combinational code relating to differing densities of Serial DataFlash devices, allowing a total of sixteen different density configurations. out Built-in Erase command to be utilized to reduce programming times when writing large amounts of data to the device. To perform a Block Erase, an opcode of 50H must be loaded into the device, followed by four reserved bits, eight address bits (PA10 - PA3), and 12 don’t care bits. The eight address bits are used to specify which block of eight pages is to be erased. When a low-to-high transition occurs on the CS pin, the part will erase the selected block of eight pages to 1s. The erase operation is internally self-timed and should take place in a maximum time of tBE. During this time, the status register will indicate that the part is busy. Additional Commands Main Memory Page to Buffer Transfer A page of data can be transferred from the main memory to either buffer 1 or buffer 2. To start the operation, an 8-bit opcode, 53H for buffer 1 and 55H for buffer 2, must be followed by the four reserved bits, 11 address bits (PA10 - PA0) which specify the page in main memory that is to be transferred, and nine don’t care bits. The CS pin must be low while toggling the SCK pin to load the opcode, the address bits, and the don’t care bits from the SI pin. The transfer of the page of data from the main memory to the buffer will begin when the CS pin transitions from a low to a high state. During the transfer of a page of data (tXFR), the status register can be read to determine whether the transfer has been completed or not.
