MAX6680 Datasheet, PDF (9/17 Pages) Maxim Integrated Products – Fail-Safe Remote/Local Temperature Sensors with SMBus Interface

±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
Write Byte Format
S
ADDRESS
WR
7 bits
Slave Address: equiva-
lent to chip-select line of
a 3-wire interface
Read Byte Format
ACK
COMMAND
ACK
8 bits
Command Byte: selects which
register you are writing to
DATA
ACK
P
8 bits
1
Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
ADDRESS WR ACK COMMAND ACK
S ADDRESS RD ACK DATA
///
P
7 bits
8 bits
7 bits
8 bits
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
Send Byte Format
ADDRESS WR
7 bits
ACK COMMAND ACK P
8 bits
Command Byte: sends com-
mand with no data, usually
used for one-shot command
S = Start condition
P = Stop condition
Shaded = Slave transmission
/// = Not acknowledged
Receive Byte Format
S ADDRESS RD
7 bits
ACK DATA ///
P
8 bits
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
Figure 3. SMBus Protocols
ture registers are not updated. The previous data is not
changed and remains available.
SMBus Digital Interface
From a software perspective, the MAX6680/MAX6681
appear as a series of 8-bit registers that contain tem-
perature data, alarm threshold values, and control bits.
A standard SMBus-compatible 2-wire serial interface is
used to read temperature data and write control bits
and alarm threshold data. The device responds to the
same SMBus slave address for access to all functions.
The MAX6680/MAX6681 employ four standard SMBus
protocols: Write Byte, Read Byte, Send Byte, and
Receive Byte (Figure 3). The shorter Receive Byte pro-
tocol allows quicker transfers, provided that the correct
data register was previously selected by a Read Byte
instruction. Use caution with the shorter protocols in
multimaster systems, since a second master could
overwrite the command byte without informing the first
master.
When the conversion rate is 8Hz, temperature data can
be read from the Read Internal Temperature (00h) and
Read External Temperature (01h) registers. The tem-
perature data format in these registers is 7 bits + sign
in two’s-complement form for each channel, with the
LSB representing 1°C (Table 2). The MSB is transmitted
first. Extended range extends the temperature data
range of the local and remote sensor to -64°C. Extended
range is activated by setting bit 3 of the Configuration
register to 1.
When the conversion rate is 4Hz or less, temperature
data can be read from the Read Internal Temperature
(00h) and Read External Temperature (01h) registers,
the same as for faster conversion rates. An additional 3
bits can be read from the Read External Extended
Temperature (10h), which extends the remote tempera-
ture data to 10 bits + sign and the resolution to 0.125°C
per LSB (Table 3).
When a conversion is complete, the Main register and
the Extended register are updated almost simultane-
ously. Ensure that no conversions are completed
between reading the Main and Extended registers so
that when data that is read by both registers contain
the result of the same conversion.
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