9

AT25DF256

DS-25DF256–035D–2/2017

Figure 7-3. Dual-Output Read Array

8.

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 12) to set the Write Enable Latch (WEL) bit of the

Status Register to a logical “1” state.

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

address bytes denoting the first byte 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 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 back to the beginning of the same page.

For 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). 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.

When the CS pin is deasserted, the device will take the data stored in the internal buffer and program it 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

The three address bytes and at least one complete byte of data must be clocked into the device before the CS pin is

deasserted, and the CS pin must be deasserted on even byte boundaries (multiples of eight bits); otherwise, the device

will abort the operation and no data will be programmed into the memory array. In addition, if the memory is in the

protected state (see “Block Protection” on page 13), then the Byte/Page Program command will not be executed, and the

device will return to the idle state once the CS pin has been deasserted. The WEL bit in the Status Register will be reset

back to the logical “0” state if the program cycle aborts due to an incomplete address being sent, an incomplete byte of

data being sent, the CS pin being deasserted on uneven byte boundaries, or because the memory location to be

programmed is protected.