CAP1208 datasheet(15/67 Pages) MICROCHIP

15 / 67 page

8-Channel Capacitive Touch Sensor

Datasheet

 2014 Microchip Technology Inc.

DS00001570B-page 15

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.

3.2.5

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 CAP1208 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 CAP1208 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, "Configuration Registers").

3.2.7

SMBus and I2C Compatibility

The major differences between SMBus and I2C devices are highlighted here. For more information,

refer to the SMBus 2.0 specification.

1. CAP1208 supports I2C fast mode at 400kHz. This covers the SMBus max time of 100kHz.

2. Minimum frequency for SMBus communications is 10kHz.

3. The SMBus client protocol will reset if the clock is held low longer than 30ms (timeout condition).

This can be enabled in the CAP1208 by setting the TIMEOUT bit in the Configuration register. I2C

does not have a timeout.

4. The SMBus client protocol will reset if both the clock and the data line are high for longer than

200us (idle condition). This can be enabled in the CAP1208 by setting the TIMEOUT bit in the

Configuration register. I2C does not have an idle condition.

5. I2C devices do not support the Alert Response Address functionality (which is optional for SMBus).

6. 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 CAP1208 supports I2C formatting only.

3.3

SMBus Protocols

The CAP1208 is SMBus 2.0 compatible and supports Write Byte, Read Byte, Send Byte, and Receive

Byte as valid protocols as shown below.

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

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