Re m o t e /Lo c a l Te m p e ra t u re S e n s o r
w it h S MBu s S e ria l In t e rfa c e
MAX61
A
B
C
D
E
F
G
H
I
J
K
L
M
t
t
HIGH
LOW
SMBCLK
SMBDATA
7
t
t
t
t
HD:DAT
HD:STA
SU:STA
SU:DAT
t
t
SU:STO
BUF
A = START CONDITION
J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION, DATA EXECUTED BY SLAVE
M = NEW START CONDITION
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
I = SLAVE PULLS SMBDATA LINE LOW
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
Figure 4. SMBus Write Timing Diagram
A
B
C
D
E
F
G
H
I
J
K
t
t
HIGH
LOW
SMBCLK
SMBDATA
t
t
t
t
t
BUF
SU:STA HD:STA
SU:DAT
SU:STO
A = START CONDITION
E = SLAVE PULLS SMBDATA LINE LOW
I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
Figure 5. SMBus Read Timing Diagram
factor proportional to that temperature. The relationship
between clock duty and temperature is fixed in a look-
up table contained in the microcontroller code.
P ro g ra m m in g Ex a m p le :
Clo c k -Th ro t t lin g Co n t ro l fo r CP Us
An untested example of pseudocode for proportional
temperature control of Intel mobile CPUs via a power-
management microcontroller is given in Listing 1. This
program consists of two main parts: an initialization rou-
tine and an interrupt handler. The initialization routine
checks for SMBus communications problems and sets
up the MAX1617 configuration and conversion rate. The
interrupt handler responds to ALERT signals by reading
the current temperature and setting a CPU clock duty
Note: Thermal management decisions should be made
based on the latest temperature obtained from the
MAX1617 rather than the value of the Status Byte. The
MAX1617 has a very quick response to changes in its
environment due to its sensitivity and its small thermal
mass. High and low alarm conditions can exist in the
Status Byte due to the MAX1617 correctly reporting
environmental changes around it.
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
