AT25DF021A datasheet(14/59 Pages) RENESAS

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DS-AT25DF021A-042 Rev. J

Page 14

12/22/22

AT25DF021A Datasheet

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 is specified. The device incorporates an internal

address counter that automatically increments 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 is 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 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 continues reading back at the beginning of the

array (000000h). No delays are incurred when wrapping around from the end of the array to the beginning of the

array.

Deasserting the CS pin terminates the read operation and put the SO pin into high-impedance state. The CS pin

can be deasserted at any time and does not require a full byte of data be read.

Figure 8. Read Array - 03h Opcode

Figure 9. Read Array - 0Bh Opcode

SCK

MSB

00000011

410 11

812

37 38

31 32

29 30

39 40

OPCODE

AAAA

AAA

MSB

DDDDDDDD

ADDRESS BITS A23-A0

DATA BYTE 1

High-Impedance

SCK

MSB

00001011

410 11

812

42 43

37 38

31 32

29 30

47 48

OPCODE

AAAA

AAA

MSB

XXXXXXXX

MSB

DDDDDDDD

ADDRESS BITS A23-A0

DON'T CARE

DATA BYTE 1

High-Impedance

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