Datasheet

SCL
SDA
START
STOP
1 2 6 7
8
9
1 2
8
9
MSB
7-bit Slave Address
R/W
Direction
Bit
Acknowledge
from the Device
MSB
Data Byte
*Acknowledge
or Not-ACK
ACK N/ACK
Repeated for the Lower Data Byte
and Additional Data Transfers
LSB LSB
Bus Activity:
Master
SDA Line
Bus Activity:
Slave
Start
Slave
Address
A
C
K
S
Address
A
C
K
S
Start
Slave
Address
A
C
K
N
A
C
K
P
Stop
Data
0 1
Register
7-bit Address 7-bit Address
A
C
K
A
C
K
A
C
K
S
P
Stop
Bus Activity:
Slave
SDA Line
Bus Activity:
Master
Slave
Address
Address Data
Start
0
Register
7-bit Address
DS90UB903Q, DS90UB904Q
SNLS332E –JUNE 2010–REVISED APRIL 2013 www.ti.com
DESCRIPTION OF BIDIRECTIONAL CONTROL BUS AND I2C MODES
The I
2
C compatible interface allows programming of the DS90UB903Q, DS90UB904Q, or an external remote
device (such as a display) through the bidirectional control channel. Register programming transactions to/from
the DS90UB903Q/904Q chipset are employed through the clock (SCL) and data (SDA) lines. These two signals
have open-drain I/Os and both lines must be pulled-up to VDDIO by external resistor. Figure 4 shows the timing
relationships of the clock (SCL) and data (SDA) signals. Pull-up resistors or current sources are required on the
SCL and SDA busses to pull them high when they are not being driven low. A logic zero is transmitted by driving
the output low. A logic high is transmitted by releasing the output and allowing it to be pulled-up externally. The
appropriate pull-up resistor values will depend upon the total bus capacitance and operating speed. The
DS90UB903Q/904Q I
2
C bus data rate supports up to 100 kbps according to I
2
C specification.
To start any data transfer, the DS90UB903Q/904Q must be configured in the proper I
2
C mode. Each device can
function as an I
2
C slave proxy or master proxy depending on the mode determined by MODE pin. The Ser/Des
interface acts as a virtual bridge between Master Controller Unit (MCU) and the remote device. When the MODE
pin is set to High, the device is treated as a slave proxy; acts as a slave on behalf of the remote slave. When
addressing a remote peripheral or Serializer/Deserializer (not wired directly to the MCU), the slave proxy will
forward any byte transactions sent by the Master controller to the target device. When MODE pin is set to Low,
the device will function as a master proxy device; acts as a master on behalf of the I
2
C master controller. Note
that the devices must have complementary settings for the MODE configuration. For example, if the Serializer
MODE pin is set to High then the Deserializer MODE pin must be set to Low and vice-versa.
Figure 25. Write Byte
Figure 26. Read Byte
Figure 27. Basic Operation
24 Submit Documentation Feedback Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: DS90UB903Q DS90UB904Q