CAP1298 datasheet(12/68 Pages) MICROCHIP

12 / 68 page

CAP1298

DS00001571B-page 12

 2013-2015 Microchip Technology Inc.

3.2.6

SMBUS TIMEOUT

The CAP1298 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.

CAP1298supports I2C fast mode at 400kHz. This covers the SMBus max time of 100kHz.

Minimum frequency for SMBus communications is 10kHz.

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

enabled in the CAP1298 by setting the TIMEOUT bit in the Configuration register. I2C does not have a timeout.

The SMBus client protocol will reset if both the clock and the data line are high for longer than 200us (idle con-

dition). This can be enabled in the CAP1298by setting the TIMEOUT bit in the Configuration register. 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 CAP1298 supports I2C formatting only.

3.3

SMBus Protocols

The CAP1298 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.

3.3.1

SMBUS WRITE BYTE

The Write Byte is used to write one byte of data to a specific register as shown in Table 3-2.

3.3.2

SMBUS READ BYTE

The Read Byte protocol is used to read one byte of data from the registers as shown in Table 3-3.

TABLE 3-1:

PROTOCOL FORMAT

Data Sent to

Device

Data Sent to the

HOst

Data sent

TABLE 3-2:

WRITE BYTE PROTOCOL

Start

Slave

Address

ACK

Address

ACK

Data

ACK

Stop

1 ->0

0101_000

XXh

0 -> 1

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