1.5°C SMBus Temperature Sensor in Miniature SOT-23

Datasheet

SMSC EMC1001

7

Revision 1.6 (01-29-07)

DATASHEET

Chapter 3 System Management Bus Interface Protocol

A host controller, such as an SMSC I/O controller, communicates with the EMC1001 via the two wire

serial interface named SMBus. The SMBus interface is used to read and write registers in the

EMC1001, which is a slave-only device. A detailed timing diagram is shown in Figure 3.1.

Figure 3.1 System Management Bus Timing Diagram

The EMC1001 implements a subset of the SMBus specification and supports Write Byte, Read Byte,

Send Byte, Receive Byte, and Alert Response Address protocols. as shown. In the tables that describe

the protocol, the “gray” columns indicate that the slave is driving the bus.

3.1

Write Byte

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

3.2

Read Byte

The Read Byte protocol is used to read one byte of data from the registers as shown below:

3.3

Send Byte

The Send Byte protocol is used to set the Internal Address Register to the correct Address. The Send

Byte can be followed by the Receive Byte protocol described below in order to read data from the

register. The send byte protocol cannot be used to write data - if data is to be written to a register then

the write byte protocol must be used as described in subsection above. The send byte protocol is shown

in Table 3.3.

Table 3.1 SMBus Write Byte Protocol

START

SLAVE ADDRESS

WR

ACK

COMMAND

ACK

DATA

ACK

STOP

17

1

18

18

11

Table 3.2 SMBus Read Byte Protocol

START

SLAVE ADDRESS

WR

ACK

COMMAND

ACK

START

SLAVE ADDRESS

RD

ACK

DATA

NACK

STOP

17

1

18

11

7

1

1

81

1

Table 3.3 SMBus Send Byte Protocol

FIELD:

START

SLAVE ADDR

WR

ACK

REG. ADDR

ACK

STOP

Bits:

17

1

1

8

1

1

SM DA TA

SM CLK

T

LO W

T

R

T

HIG H

T

F

T

BUF

T

HD :S TA

P

S

S - S tart C ondition

P - Stop Condition

T

T

SU :S TA

T

HD:S TA

P

T

SU :S TO

S