8 Channel Capacitive Touch Sensor with 8 LED Drivers
Datasheet
3.2.5
SMBus Stop Bit
The SMBus Stop bit is defined as a transition of the SMBus Data line from a logic ‘0’ state to a logic
‘1’ state while the SMBus clock line is in a logic ‘1’ state. When the CAP1088 detects an SMBus Stop
bit, and it has been communicating with the SMBus protocol, it will reset its client interface and prepare
to receive further communications.
3.2.6
SMBus Timeout
The CAP1088 includes an SMBus timeout feature. Following a 30ms period of inactivity on the SMBus
where the SMCLK pin is held low, the device will timeout and reset the SMBus interface.
The timeout function defaults to disabled. It can be enabled by setting the TIMEOUT bit in the
Configuration register (see Section 5.6).
2
3.2.7
SMBus and I C Compliance
The major difference between SMBus and I2C devices is highlighted here. For complete compliance
information refer to the SMBus 2.0 specification.
1. Minimum frequency for SMBus communications is 10kHz.
2. The client protocol will reset if the clock is held low longer than 30ms.
3. The client protocol will reset if both the clock and the data line are high for longer than 150us (idle
condition).
4. I2C devices do not support the Alert Response Address functionality (which is optional for SMBus).
5. I2C devices support block read and write differently. I2C protocol allows for unlimited number of
bytes to be sent in either direction. The SMBus protocol requires that an additional data byte
indicating number of bytes to read / write is transmitted. The CAP1088 supports I2C formatting only.
3.3
SMBus Protocols
The CAP1088 is SMBus 2.0 compatible and supports Send Byte, Read Byte, Block Read, Receive
Byte as valid protocols as shown below. The CAP1088 also supports the I2C block read and block
write protocols. Finally, it will respond to the Alert Response Address protocol but is not in full
compliance.
All of the below protocols use the convention in Table 3.2.
Table 3.2 Protocol Format
DATA SENT
TO DEVICE
DATA SENT TO
THE HOST
Data sent
Data sent
3.3.1
SMBus Write Byte
The Write Byte is used to write one byte of data to a specific register as shown in Table 3.3.
Table 3.3 Write Byte Protocol
SLAVE
ADDRESS
REGISTER
ADDRESS
REGISTER
DATA
START
1 ->0
WR
ACK
ACK
ACK
STOP
YYYY_YYY
0
0
XXh
0
XXh
0
0 -> 1
SMSC CAP1088
Revision 1.1 (08-05-09)
DATA1S7HEET
SMSC [ SMSC CORPORATION ]
