Rainbow Electronics MAX6659 - Manual (Page 9)

the conversion cycle is interrupted, and the tempera-
ture registers are not updated. The previous data is not
changed and remains available.
SMBus Digital Interface
From a software perspective, each of the MAX6657/
MAX6658/MAX6659 appears as a series of 8-bit regis-
ters that contain temperature 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 MAX6657/MAX6658/MAX6659 employ four stan-
dard SMBus protocols: Write Byte, Read Byte, Send
Byte, and Receive Byte (Figures 2, 3, and 4). The short-
er Receive Byte protocol allows quicker transfers, pro-
vided 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 with-
out informing the first master.
When the conversion rate is greater than 4Hz, temperature
data can be read from the Read Internal Temperature
(00h) and Read External Temperature (01h) registers.
The temperature data format is 7 bits + sign in two's-
complement form for each channel, with the LSB repre-
senting 1°C (Table 2). The MSB is transmitted first.
When the conversion rate is 4Hz or less, the first 8 bits
of 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) and Read Internal
Extended Temperature (11h) registers, which extends
the 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, both registers contain the
result of the same conversion.
To ensure valid extended data, read extended resolu-
tion temperature data using one of the following
approaches:
MAX6657/MAX6658/MAX6659
______________________________________________________________________________________ 9
Figure 2. SMBus Protocols
ACK
7 bits
ADDRESS ACK WR
8 bits
DATA ACK
1
P
8 bits
S COMMAND
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)
ACK
7 bits
ADDRESS ACK WR S ACK
8 bits
DATA
7 bits
ADDRESS RD
8 bits
/// P COMMAND
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
ACK
7 bits
ADDRESS WR
8 bits
COMMAND ACK P ACK
7 bits
ADDRESS RD
8 bits
DATA /// P S
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
±1°C, SMBus-Compatible Remote/Local Temperature
Sensors with Overtemperature Alarms