CAT25320

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9

READ OPERATIONS

Read from Memory Array

To read from memory, the host sends a READ instruction

followed by a 16−bit address (see Table 11 for the number

of significant address bits).

After receiving the last address bit, the CAT25320 will

respond by shifting out data on the SO pin (as shown in

Figure 9). Sequentially stored data can be read out by simply

continuing to run the clock. The internal address pointer is

automatically incremented to the next higher address as data

is shifted out. After reaching the highest memory address,

the address counter “rolls over” to the lowest memory

address, and the read cycle can be continued indefinitely.

The read operation is terminated by taking CS high.

Read Status Register

To read the status register, the host simply sends a RDSR

command. After receiving the last bit of the command, the

CAT25320 will shift out the contents of the status register on

the SO pin (Figure 10). The status register may be read at any

time, including during an internal write cycle. While the

internal write cycle is in progress, the RDSR command will

output the full content of the status register (New product,

Rev. F) or the RDY (Ready) bit only (i.e., data out = FFh) for

previous product revision C (Mature product). For easy

detection of the internal write cycle completion, both during

writing to the memory array and to the status register, we

recommend sampling the RDY bit only through the polling

routine. After detecting the RDY bit “0”, the next RDSR

instruction will always output the expected content of the

status register.

Figure 9. READ Timing

SCK

SI

SO

BYTE ADDRESS*

012

3456

78

9

7

6

5

4

3

2

1

0

DATA OUT

MSB

HIGH IMPEDANCE

OPCODE

21

20

22

23

24

25

26 27

28

29

30

00

00

0

1

1

Dashed Line = mode (1, 1)

CS

* Please check the Byte Address Table (Table 11)

0

10

Figure 10. RDSR Timing

01

2

3

4

5

6

7

8

10

911

12

13

14

SCK

SI

DATA OUT

MSB

HIGH IMPEDANCE

OPCODE

SO

7

6

5

4

3

2

1

0

00

0

0

0

1

0

1

Dashed Line = mode (1, 1)

CS