EMC2104 datasheet(18/101 Pages) SMSC

18 / 101 page

Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown

Datasheet

Revision 1.74 (05-08-08)

SMSC EMC2104

DATASHEET

Chapter 4 Communications

4.1

System Management Bus Interface Protocol

The EMC2104 communicates with a host controller, such as an SMSC 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 4.1. Stretching of the SMCLK signal is supported,

however the EMC2104 will not stretch the clock signal.

The EMC2104 powers up as an SMBus client.

The EMC2104 contains a single SMBus interface. The SMBus address is determined by the

ADDR_SEL pin (see Section 4.7)The EMC2104 client interfaces are SMBus 2.0 compatible and

support Send Byte, Read Byte, Receive Byte and the Alert Response Address as valid protocols.

These protocols are used as shown below.

All of the below protocols use the convention in Table 4.1.

4.2

Write Byte

The Write Byte is used to write one byte of data to the registers as shown below Table 4.2:

Figure 4.1 SMBus Timing Diagram

Table 4.1 Protocol Format

DATA SENT

TO DEVICE

DATA SENT TO

THE HOST

# of bits sent

Table 4.2 Write Byte Protocol

START

SLAVE

ADDRESS

ACK

ADDRESS

ACK

DATA

ACK

STOP

0 -> 1

0101_111

XXh

1 -> 0

SMDATA

SMCLK

TLOW

TRISE

THIGH

TFALL

TBUF

THD:STA

S - Start Condition

P - Stop Condition

THD:DAT

TSU:DAT

TSU:STA

THD:STA

TSU:STO

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