Multiple Channel Capacitive Touch Sensor and LED Driver
Datasheet
3.1.4
SMBus ACK and NACK Bits
The SMBus client will acknowledge all data bytes that it receives. This is done by the client device
pulling the SMBus Data line low after the 8th bit of each byte that is transmitted. This applies to both
the Write Byte and Block Write protocols
The Host will NACK (not acknowledge) the last data byte to be received from the client by holding the
SMBus data line high after the 8th data bit has been sent. For the Block Read protocol, the Host will
ACK each data byte that it receives except the last data byte.
3.1.5
3.1.6
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 CAP1014 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.
SMBus Time-out
The CAP1014 includes an SMBus time-out feature. Following a 30ms period of inactivity on the SMBus
where the SMCLK pin is held low, the device will time-out and reset the SMBus interface.
The time-out function defaults to disabled. It can be enabled by setting the TIMEOUT bit in the
Configuration register (see Section 5.14).
2
3.1.7
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).
3.2
SMBus Protocols
The CAP1014 is SMBus 2.0 compatible and supports Send Byte, Read Byte, Block Read, Receive
Byte as valid protocols as shown below. The CAP1014 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 3.1.
Table 3.1 Protocol Format
DATA SENT
TO DEVICE
DATA SENT TO
THE HOST
Data sent
Data sent
Revision 1.65 (08-11-09)
SMSC CAP1014
DATA1S6HEET
SMSC [ SMSC CORPORATION ]
