Rainbow Electronics MAX6649 - Manual (Page 7)

MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensor with Overtemperature Alarms
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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. Alarm Threshold Registers
Four registers store ALERT threshold values—one high-
temperature (T
HIGH ) and one low-temperature (T LOW )
register each for the local and remote channels. If
either measured temperature equals or exceeds the
corresponding ALERT threshold value, the ALERT inter-
rupt asserts.
SMBCLK
A B C D E F G H I J K
SMBDATA
t SU:STA
t HD:STA
t LOW t HIGH
t SU:DAT t HD:DAT t SU:STO t BUF
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 WR ACK COMMAND
7 bits 8 bits
ACK DATA
8 bits
ACK P
1
S ADDRESS WR ACK COMMAND ACK S ADDRESS RD ACK DATA /// P
8 bits 7 bits 8 bits 7 bits
S ADDRESS WR ACK COMMAND ACK P
7 bits 8 bits
S ADDRESS RD ACK DATA /// P
8 bits 7 bits