EMC2302 datasheet(13/44 Pages) SMSC

13 / 44 page

Dual RPM-Based PWM Fan Controller

Datasheet

SMSC EMC2302

Revision 1.1 (10-12-09)

DATASHEET

3.1.5

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 EMC2302 detects an SMBus Stop

bit has been communicating with the SMBus protocol, it will reset its client interface and prepare to

receive further communications.

3.1.6

SMBus Time-out

The EMC2302 includes an SMBus timeout feature. Following a 30ms period of inactivity on the

SMBus, the device will time-out and reset the SMBus interface.

The SMBus timeout feature is disabled by default and can be enabled via clearing the DIS_TO bit in

the Configuration register (20h).

3.1.7

SMBus and I2C Compliance

The major difference between SMBus and I2C devices is highlighted here. For complete compliance

information refer to the SMBus 2.0 specification.

1. Minimum frequency for SMBus communications is 10kHz (I2C has no minimum frequency).

2. The slave protocol will reset if the clock is held low for longer than 30ms (I2C has no timeout).

3. The slave protocol will reset if both the clock and data lines are held high for longer than 150us.

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

5. The Block Read and Block Write protocols are only compliant with I2C data formatting. They do

not support SMBus formatting for Block Read and Block Write protocols.

3.2

SMBus Protocols

The EMC2302 is SMBus 2.0 compatible and supports Send Byte, Read Byte, Receive Byte and Write

Byte as valid protocols as shown below. It will respond to the Alert Response Address protocol but is

not in full compliance.

All of the below protocols use the convention in Table 3.1. When reading the protocol blocks, the value

of YYYY_YYYb should be replaced with the respective SMBus addresses.

3.2.1

Write Byte

The Write Byte is used to write one byte of data to the registers as shown below Table 3.2.

Table 3.1 Protocol Format

DATA SENT

TO DEVICE

DATA SENT TO

THE HOST

# of bits sent

Table 3.2 Write Byte Protocol

START

SLAVE

ADDRESS

ACK

ADDRESS

ACK

DATA

ACK

STOP

1 -> 0

YYYY_YYYb

XXh

0 -> 1

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