Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
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.
TLOW
THIGH
THD:STA
TSU:STO
TRISE
TFALL
SMCLK
TSU:STA
THD:STA
THD:DAT
TSU:DAT
SMDATA
TBUF
S
S
P
P - Stop Condition
P
S - Start Condition
Figure 4.1 SMBus Timing Diagram
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.
Table 4.1 Protocol Format
DATA SENT
TO DEVICE
DATA SENT TO
THE HOST
# of bits sent
# of bits sent
4.2
Write Byte
The Write Byte is used to write one byte of data to the registers as shown below Table 4.2:
Table 4.2 Write Byte Protocol
SLAVE
ADDRESS
REGISTER
ADDRESS
REGISTER
DATA
START
WR
ACK
ACK
ACK
STOP
0 -> 1
0101_111
0
0
XXh
0
XXh
0
1 -> 0
Revision 1.74 (05-08-08)
SMSC EMC2104
DATA1S8HEET
SMSC [ SMSC CORPORATION ]
