the address bytes from the input pin (SI). On the low-to-high transition of the CS pin, the data
bytes in the selected main memory page will be compared with the data bytes in buffer 1 or
buffer 2. During this time (tCOMP), the status register will indicate that the part is busy. On com-
pletion of the compare operation, bit 6 of the status register is updated with the result of the
compare.
11.3 Auto Page Rewrite
This mode is only needed if multiple bytes within a page or multiple pages of data are modified in
a random fashion within a sector. This mode is a combination of two operations: Main Memory
Page to Buffer Transfer and Buffer to Main Memory Page Program with Built-in Erase. A page of
data is first transferred from the main memory to buffer 1 or buffer 2, and then the same data
(from buffer 1 or buffer 2) is programmed back into its original page of main memory. To start the
rewrite operation for the DataFlash standard page size (264 bytes), a 1-byte opcode, 58H for
buffer 1 or 59H for buffer 2, must be clocked into the device, followed by three address bytes
comprised of 4 don’t care bits, 11 page address bits (PA10-PA0) that specify the page in main
memory to be rewritten and 9 don’t care bits. To initiate an auto page rewrite for a binary page
size (256 bytes), the opcode 58H for buffer 1 or 59H for buffer 2, must be clocked into the device
followed by three address bytes consisting of 5 don’t care bits, 11 page address bits (A18 - A8)
that specify the page in the main memory that is to be written and 8 don’t care bits. When a low-
to-high transition occurs on the CS pin, the part will first transfer data from the page in main
memory to a buffer and then program the data from the buffer back into same page of main
memory. The operation is internally self-timed and should take place in a maximum time of tEP.
During this time, the status register will indicate that the part is busy.
If a sector is programmed or reprogrammed sequentially page by page, then the programming
algorithm shown in Figure 25-1 (page 45) is recommended. Otherwise, if multiple bytes in a
page or several pages are programmed randomly in a sector, then the programming algorithm
shown in Figure 25-2 (page 46) is recommended. Each page within a sector must be
updated/rewritten at least once within every 10,000 cumulative page erase/program operations
in that sector.
11.4 Status Register Read
The status register can be used to determine the device’s ready/busy status, page size, a Main
Memory Page to Buffer Compare operation result, the Sector Protection status or the device
density. The Status Register can be read at any time, including during an internally self-timed
program or erase operation. To read the status register, the CS pin must be asserted and the
opcode of D7H must be loaded into the device. After the opcode is clocked in, the 1-byte status
register will be clocked out on the output pin (SO), starting with the next clock cycle. The data in
the status register, starting with the MSB (bit 7), will be clocked out on the SO pin during the next
eight clock cycles. After the one byte of the status register has been clocked out, the sequence
will repeat itself (as long as CS remains low and SCK is being toggled). The data in the status
register is constantly updated, so each repeating sequence will output new data.
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. Since the data in the status register is constantly updated, the user must toggle SCK pin to
check the ready/busy status. There are several 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, Main Memory Page Program through Buffer, Page
Erase, Block Erase, Sector Erase, Chip Erase and Auto Page Rewrite.
22
AT45DB041D
3595L–DFLASH–4/08
ATMEL [ ATMEL ]
