Precision SMBus-Compatible Remote/Local

Temperature Sensors with Overtemperature Alarms

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7

2) If the MAX6648/MAX6692 are in run mode, read the

status byte. If the BUSY bit indicates that a conversion

is in progress, wait until the conversion is complete

(BUSY bit set to zero) before reading the temperature

data. Following a conversion completion, immediately

read the contents of the temperature data registers. If

no conversion is in progress, the data can be read

within a few microseconds, which is a sufficiently short

period of time to ensure that a new conversion cannot

be completed until after the data has been read.

SMBCLK

AB

C

D

E

FG

H

I

J

K

SMBDATA

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

E = SLAVE PULLS SMBDATA LINE LOW

L

M

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO MASTER

H = LSB OF DATA CLOCKED INTO MASTER

I = MASTER PULLS DATA LINE LOW

J = ACKNOWLEDGE CLOCKED INTO SLAVE

K = ACKNOWLEDGE CLOCK PULSE

L = STOP CONDITION

M = NEW START CONDITION

Figure 2. SMBus Write Timing Diagram

Write Byte Format

Read Byte Format

Send Byte Format

Receive Byte Format

Slave Address: equiva-

lent to chip-select line of

a 3-wire interface

Command Byte: selects which

register you are writing to

Data Byte: data goes into the register

set by the command byte (to set

thresholds, configuration masks, and

sampling rate)

Slave Address: equiva-

lent to chip-select line

Command Byte: selects

which register you are

reading from

Slave Address: repeated

due to change in data-

flow direction

Data Byte: reads from

the register set by the

command byte

Command Byte: sends com-

mand with no data, usually

used for one-shot command

Data Byte: reads data from

the register commanded

by the last Read Byte or

Write Byte transmission;

also used for SMBus Alert

Response return address

S = Start condition

Shaded = Slave transmission

P = Stop condition

/// = Not acknowledged

Figure 1. SMBus Protocols

S

ADDRESS

RD

ACK

DATA

///

P

7 bits

8 bits

WR

S

ACK

COMMAND

ACK

P

8 bits

ADDRESS

7 bits

P

1

ACK

DATA

8 bits

ACK

COMMAND

8 bits

ACK

WR

ADDRESS

7 bits

S

S

ADDRESS

WR

ACK

COMMAND

ACK

S

ADDRESS

7 bits

8 bits

7 bits

RD

ACK

DATA

8 bits

///

P