3.3V Uniform Sector

Standard and Dual Serial Flash

GD25D40C/20C

23

followed by the 24-bit device identification, stored in the memory. Each bit is shifted out on the falling edge of Serial Clock.

The command sequence is shown in Figure17. The Read Identification (RDID) command is terminated by driving CS# high

at any time during data output. When CS# is driven high, the device is in the Standby Mode. Once in the Standby Mode,

the device waits to be selected, so that it can receive, decode and execute commands.

Figure17. Read Identification ID Sequence Diagram

7.17.

Read Unique ID (4BH)

The Read Unique ID command accesses a factory-set read-only 128bit number that is unique to each device. The

Unique ID can be used in conjunction with user software methods to help prevent copying or cloning of a system.

The Read Unique ID command sequence: CS# goes low  sending Read Unique ID command  3-Byte Address

(000000H) Dummy Byte128bit Unique ID Out CS# goes high.

Figure18. Read Unique ID Sequence Diagram

Command

0

1

2

3

4

5

6

7

4BH

CS#

SCLK

SI

SO

High-Z

8

9 10

28 29 30 31

3

2

1

0

23 22 21

24-bit address

MSB

34 35 36 37

33

6

5

4

3

2

1

0

38 39

Data Out1

32

42 43 44 45

41

46 47

40

7

6

5

4

3

2

1

0

7

6

5

7

Data Out2

CS#

SCLK

SI

SO

MSB

Dummy Byte

0

1

2

3

4

5

6

7

CS#

SCLK

SI

SO

8

9 10

MSB

18 19 20 21

17

6

5

4

3

2

1

0

22 23

16

26 27 28 29

25

30 31

24

7

Capacity

JDID7-JDID0

CS#

SCLK

SI

SO

MSB

Memory Type

JDID15-JDID8

6

5

4

3

2

1

0

7

11 12 13 14 15

9FH

6

5

4

3

2

1

0

7

Manufacturer ID

MSB

Command