STw4102

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10

10.1

Read and write operations

data line (SDA) and a serial clock line (SCL):

SCL: input clock used to shift data

SDA: input/output bi-directional data transfers

A filter rejects the potential spikes on the bus data line to preserve data integrity. The bi-

directional data line supports transfers up to 400 kbit/s (fast-mode). The data is shifted into

and from the chip on the SDA line, MSB first.

The first bit must be high (START), followed by the Device ID and Read/Write control bit (see

Table 15). The AddrID0 to AddrID2 bits are factory programmable, their default ID value is

70h (AddrID0 = AddrID1 = AddrID2 = 0). Then, the STw4102 sends an acknowledge at the

end of the 8-bit transmission.

The next 8 bits correspond to the address register, followed by another acknowledge.

Table 16 shows the address register format.

The data field is sent last. It can be composed of several 8-bit data registers, each followed

by an acknowledge. Table 17 shows the data register format.

The STw4102 supports byte read, word read, block read, and byte write operations. The

transmission protocol is summarized in Figure 24 and Figure 25.

r

Figure 24.

Byte, word and block read operation

Table 15.

Device ID and R/W bit format

b7

b6

b5

b4

b3

b2

b1

b0

1

1

1

0

AddrID2

AddrID1

AddrID0

R/W

Table 16.

Address register format

b7

b6

b5

b4

b3

b2

b1

b0

RegAddr7

RegAddr6

RegAddr5

RegAddr4

RegAddr3

RegAddr2

RegAddr1

RegAddr0

Table 17.

Data register format

b7

b6

b5

b4

b3

b2

b1

b0

DATA7

DATA6

DATA5

DATA4

DATA3

DATA2

DATA1

DATA0

Start bit = SDAfalling when SCL=1

Stop bit = SDArising when SCL=1

Restart bit = start after a start

Acknowledge = SDA force low during a SCL clock

Start Device id

Reg address

8bits

A

Restart Device id

R

A

Reg data

8bits

A

Reg data

8bits

A

Reg data

8bits

A/A

address

7 bits

7 bits

n+1

address

n+2

Stop

A

W

Master

Slave

<-- byte read -->

<-- word read (2 bytes) ---------->

<-- block read (up to 10 bytes) ---------------------->