CAP1126 datasheet(13/73 Pages) MICROCHIP

13 / 73 page

 2015 Microchip Technology Inc.

DS00001623B-page 13

CAP1126

CAP1126 supports I2C fast mode at 400kHz. This covers the SMBus max time of 100kHz.

Minimum frequency for SMBus communications is 10kHz.

The SMBus slave protocol will reset if the clock is held at a logic ‘0’ for longer than 30ms. This timeout function-

ality is disabled by default in the CAP1126 and can be enabled by writing to the TIMEOUT bit. I2C does not have

a timeout.

The SMBus slave protocol will reset if both the clock and data lines are held at a logic ‘1’ for longer than 200µs

(idle condition). This function is disabled by default in the CAP1126 and can be enabled by writing to the TIME-

OUT bit. I2C does not have an idle condition.

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

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 CAP1126 supports I2C formatting only.

4.3

SMBus Protocols

The CAP1126 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 4-2.

4.3.1

SMBUS WRITE BYTE

The Write Byte is used to write one byte of data to a specific register as shown in Table 4-3.

4.3.2

SMBUS READ BYTE

The Read Byte protocol is used to read one byte of data from the registers as shown in Table 4-4.

4.3.3

SMBUS SEND BYTE

The Send Byte protocol is used to set the internal address register pointer to the correct address location. No data is

transferred during the Send Byte protocol as shown in Table 4-5.

APPLICATION NOTE: The Send Byte protocol is not functional in Deep Sleep (i.e., DSLEEP bit is set).

TABLE 4-2:

PROTOCOL FORMAT

Data Sent to

Device

Data Sent to the

HOst

Data sent

TABLE 4-3:

WRITE BYTE PROTOCOL

Start

Slave

Address

ACK

Address

ACK

Stop

1 ->0

YYYY_YYY

XXh

0 -> 1

TABLE 4-4:

READ BYTE PROTOCOL

Start

Slave

Address

ACK

Address

ACK

Start

Slave

Address

ACK

Data

NACK

Stop

1->0

YYYY_YYY

XXh

1 ->0

YYYY_YYY

XXh

0 -> 1

TABLE 4-5:

SEND BYTE PROTOCOL

Start

Slave Address

ACK

Stop

1 -> 0

YYYY_YYY

XXh

0 -> 1

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