AT25DF641A datasheet(13/58 Pages) DIALOG

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AT25DF641A [DATASHEET]

8793F–DFLASH–11/2017

Program and Erase Commands

8.1

Byte/Page Program

The Byte/Page Program command allows anywhere from a single byte of data to 256 bytes of data to be programmed

into previously erased memory locations. An erased memory location is one that has all eight bits set to the Logical 1

state (a byte value of FFh). Before a Byte/page Program command can be started, the Write Enable command must

have been previously issued to the device (see “Write Enable” on page 21) to set the Write Enable Latch (WEL) bit of the

Status Register to a Logical 1 state.

Note:

The internal programming operation of the AT25DF641A occurs on a nibble-wide basis, and all four bits of

the nibble must be in an erased state (Logic 1 state) prior to the programming of any of the four bits. If any

one of the four bits is in the programmed state (Logic 0 state) and an attempt is made to program one of the

other four bits in the nibble from a Logic 1 to a Logic 0, then the contents of the nibble cannot be guaranteed

and may contain erroneous data.

Example 1: A 4KB Block Erase is performed to erase the first 4KB block of memory (all bytes set to FFh). The

application then programs the first byte location with a value of 7Fh (0111 1111). Without erasing the 4KB

block again, the application then attempts to program the same byte location with BFh (1011 1111)

expecting that the resulting byte value stored in memory will be 3Fh (0011 1111). However, because of the

way the AT25DF641A programs bytes internally and because all four bits of the most-significant nibble were

not in the erased state prior to the programming of the BFh value, the most-significant nibble will not contain

the value of 0011b but will instead contain a different value.

Example 2: A 4KB Block Erase is performed to erase the first 4KB block of memory (all bytes set to FFh). The

application then programs the first byte location with a value of 7Fh (0111 1111). Without erasing the 4KB

block again, the application then attempts to program the same byte location with FCh (1111 1100),

expecting that the resulting byte value stored in memory will be 7Ch (0111 1100). The resulting byte value

stored in the memory will indeed be 7Ch because no additional bits in the most-significant nibble were being

programmed from a Logic 1 to a Logic 0, and all four bits in the least-significant nibble were in the erased

state prior to the programming of the 7Ch byte value.

To perform a Byte/Page Program command, a 02h opcode must be clocked into the device followed by the three address

bytes denoting the first location of the memory array to begin programming at. After the address bytes have been clocked

in, data can then be clocked into the device and will be stored in an internal buffer.

If the starting memory address denoted by A23-A0 does not fall on an even 256-byte page boundary (A7-A0 are not

all 0), then special circumstances regarding which memory locations are to be programmed will apply. In this situation,

any data that is sent to the device that goes beyond the end of the page will wrap around to the beginning of the same

page. In addition, if more than 256 bytes of data are sent to the device, then only the last 256 bytes sent will be latched

into the internal buffer.

Example:

If the starting address denoted by A23-A0 is 0000FEh, and three bytes of data are sent to the device, then

the first two bytes of data will be programmed at addresses 0000FEh and 0000FFh, while the last byte of

data will be programmed at address 000000h. The remaining bytes in the page (addresses 000001h

through 0000FDh) will not be programmed and will remain in the erased state (FFh).

When the CS pin is deasserted, the device will take the data stored in the internal buffer into the appropriate memory

array locations based on the starting address specified by A23-A0 and the number of data bytes sent to the device. If

less than 256 bytes of data were sent to the device, then the remaining bytes within the page will not be programmed and

will remain in the erased state (FFh). The programming of the data bytes is internally self-timed and should take place in

a time of tPP or tBP if only programming a single byte.

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