AT25DF021_09 datasheet(8/41 Pages) ATMEL

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3677D–DFLASH–04/09

AT25DF021

7. Read Commands

7.1

Read Array

The Read Array command can be used to sequentially read a continuous stream of data from

the device by simply providing the clock signal once the initial starting address has been speci-

fied. The device incorporates an internal address counter that automatically increments on every

clock cycle.

Two opcodes (0Bh and 03h) can be used for the Read Array command. The use of each

opcode depends on the maximum clock frequency that will be used to read data from the

device. The 0Bh opcode can be used at any clock frequency up to the maximum specified by

fCLK, and the 03h opcode can be used for lower frequency read operations up to the maximum

specified by fRDLF.

To perform the Read Array operation, the CS pin must first be asserted and the appropriate

opcode (0Bh or 03h) must be clocked into the device. After the opcode has been clocked in, the

three address bytes must be clocked in to specify the starting address location of the first byte to

read within the memory array. Following the three address bytes, an additional dummy byte

needs to be clocked into the device if the 0Bh opcode is used for the Read Array operation.

After the three address bytes (and the dummy byte if using opcode 0Bh) have been clocked in,

additional clock cycles will result in data being output on the SO pin. The data is always output

with the MSB of a byte first. When the last byte (03FFFFh) of the memory array has been read,

the device will continue reading back at the beginning of the array (000000h). No delays will be

incurred when wrapping around from the end of the array to the beginning of the array.

Deasserting the CS pin will terminate the read operation and put the SO pin into a high-imped-

ance state. The CS pin can be deasserted at any time and does not require that a full byte of

data be read.

Figure 7-1.

Read Array - 0Bh Opcode

Figure 7-2.

Read Array - 03h Opcode

SCK

MSB

00001011

410 11

812

42 43

37 38

31 32

29 30

47 48

OPCODE

AAAA

AAA

MSB

XXXXXXX

MSB

DDDDDDD

ADDRESS BITS A23-A0

DON'T CARE

DATA BYTE 1

HIGH-IMPEDANCE

SCK

MSB

00000011

410 11

812

37 38

31 32

29 30

39 40

OPCODE

AAAA

AAA

MSB

DDDDDDD

ADDRESS BITS A23-A0

DATA BYTE 1

HIGH-IMPEDANCE

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