TCS3404, TCS3414
DIGITAL COLOR SENSORS
TAOS137A − APRIL 2011
SMBus and I2C Protocols
Each Send and Write protocol is, essentially, a series of bytes. A byte sent to the TCS3404/14 with the most
significant bit (MSB) equal to 1 will be interpreted as a COMMAND byte. The lower four bits of the COMMAND
byte form the register select address (see Table 1), which is used to select the destination for the subsequent
byte(s) received. The TCS3404/14 responds to any Receive Byte requests with the contents of the register
specified by the stored register select address.
The TCS3404/14 implements the following protocols of the SMB 2.0 specification:
D
D
D
D
D
D
D
Send Byte Protocol
Receive Byte Protocol
Write Byte Protocol
Write Word Protocol
Read Word Protocol
Block Write Protocol
Block Read Protocol
2
The TCS3404/14 implements the following protocols of the I C specification:
2
D
D
I C Write Protocol
2
I C Read (Combined Format) Protocol
When an SMBus Block Write or Block Read is initiated (see description of COMMAND Register), the byte
following the COMMAND byte is ignored but is a requirement of the SMBus specification. This field contains
the byte count (i.e. the number of bytes to be transferred). The TCS3404 (SMBus) device ignores this field and
extracts this information by counting the actual number of bytes transferred before the Stop condition is
detected.
2
2
When an I C Write or I C Read (Combined Format) is initiated, the byte count is also ignored but follows the
2
SMBus protocol specification. Data bytes continue to be transferred from the TCS3414 (I C) device to Master
until a NACK is sent by the Master.
The data formats supported by the TCS3404 and TCS3414 devices are:
2
D
D
Master transmitter transmits to slave receiver (SMBus and I C):
−
The transfer direction in this case is not changed.
Master reads slave immediately after the first byte (SMBus only):
−
At the moment of the first acknowledgment (provided by the slave receiver) the master transmitter
becomes a master receiver and the slave receiver becomes a slave transmitter.
2
D
Combined format (SMBus and I C):
−
During a change of direction within a transfer, the master repeats both a START condition and the slave
address but with the R/W bit reversed. In this case, the master receiver terminates the transfer by
generating a NACK on the last byte of the transfer and a STOP condition.
For a complete description of SMBus protocols, please review the SMBus Specification at
2
2
http://www.smbus.org/specs. For a complete description of the I C protocol, please review the NXP I C design
specification at http://www.i2c−bus.org/references/.
Copyright E 2011, TAOS Inc.
The LUMENOLOGY r Company
r
r
10
www.taosinc.com
TAOS [ TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS ]
