DIA1412

Version 1.0, Jul 2024

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11. Communication Protocol and SMBus Protocol

11.1. Communication protocol

Through the SMBus (or I2C), the DIA1412 can communicate with the host controller. The SMBus is a two-wire

serial communication protocol between a computer host and its peripheral devices. The details can be found in

Figure 1.

11.1.1. SMBus address and RD/

——

WR bit

The SMBus address byte consists of the 7-bit client address followed by the RD/

——

WR indicator bit. To the client

device, the RD/

——

WR bit can be either writing or reading date.

When the RD/

——

WR bit is a logic ‘0’, the SMBus host is writing data. When the RD/

——

WR bit is a logic ‘1’, the SMBus

host is reading data.

The DIA1412C SMBus slave address is determined by the pull-up resistor on the

______

THERM/ADDR pin as shown

in table 5 in section 9.8 "Programming SMBus (or I2C) Address".

11.1.2. SMBus data bytes

All SMBus data bytes are composed of 8-bits of information and sent in order of priority, which means they are

sent most significant bit at first.

11.1.3. SMBus ACK and NACK bits

All received data bytes are acknowledged by the SMBus client. This is accomplished by the client device pulling

the SMBus data line low after each sent byte's eighth bit. This is true of the Write Byte protocol.

By keeping the SMBus data line high after the 8th data bit has been sent, the host will NACK (not acknowledge)

the final data byte that has been received from the client.

11.1.4. SMBus timeout

SMBus timeout function is supported by the DIA1412. The device resets its SMBus protocol if the clock line is

maintained low for more than 30 ms. Setting the TIMEOUT bit in the consecutive ALERT register (see section

12.11) will enable this function.

11.1.5. SMBus and I2C compatibility

SMBus and I2C are both supported by the DIA1412. Here shows the key differences between SMBus and I2C

devices.

The DIA1412 supports I2C fast mode at 400 kHz, covering 100 kHz (maximum SMBus time).

(1) 10 kHz is the minimum frequency for SMBus communications.

(2) The condition of resetting the SMBus client protocol is that the clock is kept at a logic “0” for longer than 30

ms. The timeout functionality is disabled by default while it is enabled by writing to the bit 7 in the consecutive

ALERT register (TIMEOUT bit). I2C doesn’t have a timeout.

(3) I2C devices can’t support the ALERT response address functionality and it’s optional for SMBus.

The DIA1412 SMBus interface will not respond to signals sent with an invalid slave address or an invalid