CAP1214 datasheet(19/107 Pages) MICROCHIP

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Multiple Channel Capacitive Touch Sensor and LED Driver

Datasheet

SMSC CAP1214

Revision 1.0 (08-30-10)

DATASHEET

4.1.4

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.

4.1.5

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 CAP1214 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.

4.1.6

SMBus Time-out

The CAP1214 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 6.14).

4.1.7

SMBus and I2C Compliance

The major differences between SMBus and I2C devices are highlighted here. For complete compliance

information, refer to the SMBus 2.0 specification.

1. Minimum frequency for SMBus communications is 10kHz. There is no minimum frequency for I2C.

2. For SMBus communications, the client protocol will reset if the clock is held low longer than 30ms.

3. For SMBus communications, the client protocol will reset if both the clock and the data line are

high for longer than 400us (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.

Note: The CAP1214 supports the I2C block read and write only.

4.2

SMBus Protocols

The CAP1214 is SMBus 2.0 compatible and supports Send Byte, Read Byte, Block Read, Receive

Byte as valid protocols as shown below. The CAP1214 also supports the I2C block read and block

write protocols.

All of the below protocols use the convention in Table 4.1.

Table 4.1 Protocol Format

DATA SENT

TO DEVICE

DATA SENT TO

THE HOST

Data sent

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