CAP1208 datasheet(14/67 Pages) MICROCHIP

14 / 67 page

8-Channel Capacitive Touch Sensor

Datasheet

DS00001570B-page 14

 2014 Microchip Technology Inc.

Chapter 3 Communications

3.1

Communications

The CAP1208 communicates using the SMBus or I2C protocol.

3.2

System Management Bus

The CAP1208 communicates with a host controller, such as an MCHP SIO, through the SMBus. The

SMBus is a two-wire serial communication protocol between a computer host and its peripheral

devices. A detailed timing diagram is shown in Figure 3.1. Stretching of the SMCLK signal is supported;

however, the CAP1208 will not stretch the clock signal.

3.2.1

SMBus Start Bit

The SMBus Start bit is defined as a transition of the SMBus Data line from a logic ‘1’ state to a logic

‘0’ state while the SMBus Clock line is in a logic ‘1’ state.

3.2.2

SMBus Address and RD / WR Bit

The SMBus Address Byte consists of the 7-bit client address followed by the RD / WR indicator bit. If

this RD / WR bit is a logic ‘0’, then the SMBus Host is writing data to the client device. If this RD / WR

bit is a logic ‘1’, then the SMBus Host is reading data from the client device.

The CAP1208-1 responds to SMBus address 0101_000(r/w). The CAP1208-2 responds to the SMBus

address 0101_001(r/w).

3.2.3

SMBus Data Bytes

All SMBus Data bytes are sent most significant bit first and composed of 8-bits of information.

3.2.4

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.

Figure 3.1 SMBus Timing Diagram

SM D A TA

SM C LK

BU F

S - Start C o ndition

P - Stop C ondition

T HIGH

T LOW

HD :STA

SU :STO

HD :STA

HD :D AT

SU:D AT

SU :STA

FALL

RISE

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