6

1937J–DFLSH–9/05

AT45DB021B

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

that 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

AT45DB021B, the four bits are 0, 1, 0 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.

5.2

Program and Erase Commands

5.2.1

Buffer Write

Data can be shifted in from the SI pin into either buffer 1 or buffer 2. To load data into either

buffer, an 8-bit opcode, 84H for buffer 1 or 87H for buffer 2, must be followed by 15 don't care

bits and nine address bits (BFA8-BFA0). The nine address bits specify the first byte in the buffer

to be written. The data is entered following the address bits. If the end of the data buffer is

reached, the device will wrap around back to the beginning of the buffer. Data will continue to be

loaded into the buffer until a low-to-high transition is detected on the CS pin.

5.2.2

Buffer to Main Memory Page Program with Built-in Erase

Data written into either buffer 1 or buffer 2 can be programmed into the main memory. To start

the operation, an 8-bit opcode (83H for buffer 1 or 86H for buffer 2) must be followed by the five

reserved bits, 10 address bits (PA9-PA0) that specify the page in the main memory to be writ-

ten, and nine additional don’t care bits. When a low-to-high transition occurs on the CS pin, the

part will first erase the selected page in main memory to all 1s and then program the data stored

in the buffer into the specified page in the main memory. Both the erase and the programming of

the page are internally self-timed and should take place in a maximum time of t

time, the status register will indicate that the part is busy.

5.2.3

Buffer to Main Memory Page Program without Built-in Erase

A previously erased page within main memory can be programmed with the contents of either

buffer 1 or buffer 2. To start the operation, an 8-bit opcode (88H for buffer 1 or 89H for buffer 2)

must be followed by the five reserved bits, 10 address bits (PA9-PA0) that specify the page in

the main memory to be written, and nine additional don’t care bits. When a low-to-high transition

occurs on the CS pin, the part will program the data stored in the buffer into the specified page in

the main memory. It is necessary that the page in main memory that is being programmed has

been previously erased. The programming of the page is internally self-timed and should take

busy.

Successive page programming operations without doing a page erase are not recommended. In

other words, changing bytes within a page from a “1” to a “0” during multiple page programming

operations without erasing that page is not recommended.