DS90UB921-Q1 Datasheet, PDF (28/57 Pages) Texas Instruments – 5 - 96 MHz 24-bit Color FPD-Link III Serializer with Bidirectional Control Channel

DS90UB921-Q1
SNLS488 – MARCH 2016
www.ti.com
The Serial Bus protocol is controlled by START, START-Repeated, and STOP phases. A START occurs when
SCL transitions Low while SDA is High. A STOP occurs when SDA transition High while SCL is also HIGH. See
Figure 23.
SDA
SCL
S
START condition, or
START repeat condition
Figure 23. Start and Stop Conditions
P
STOP condition
To communicate with a remote device, the host controller (master) sends the slave address and listens for a
response from the slave. This response is referred to as an acknowledge bit (ACK). If a slave on the bus is
addressed correctly, it Acknowledges (ACKs) the master by driving the SDA bus low. If the address doesn't
match a device's slave address, it Not-acknowledges (NACKs) the master by letting SDA be pulled High. ACKs
also occur on the bus when data is being transmitted. When the master is writing data, the slave ACKs after
every data byte is successfully received. When the master is reading data, the master ACKs after every data
byte is received to let the slave know it wants to receive another data byte. When the master wants to stop
reading, it NACKs after the last data byte and creates a stop condition on the bus. All communication on the bus
begins with either a Start condition or a Repeated Start condition. All communication on the bus ends with a Stop
condition. A READ is shown in Figure 24 and a WRITE is shown in Figure 25.
If the Serial Bus is not required, the three pins may be left open (NC).
Slave Address
Register Address
S
A
2
A
1
A
0
a
0
c
k
a
c
k
S
Slave Address
a
AA
21
A
0
1
c
k
Data
a
c
k
P
Figure 24. Serial Control Bus — Read
Slave Address
Register Address
S
A
2
A
1
A
0
a
0
c
k
a
c
k
Data
a
c
k
P
Figure 25. Serial Control Bus — Write
7.6 Register Maps
28
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