Rainbow Electronics MAX1619 - Manual (Page 10)

the MAX1619 can be forced to perform A/D conversions
via the one-shot command, despite the RUN/STOP bit
being high.
Activate hardware standby mode by forcing the STBY
pin low. In a notebook computer, this line may be con-
nected to the system SUSTAT# suspend-state signal.
The STBY pin low state overrides any software conversion
command. If a hardware or software standby command
is received while a conversion is in progress, the conver-
sion cycle is truncated, and the data from that conversion
is not latched into either temperature reading register.
The previous data is not changed and remains available.
The OVERT output continues to function in both hard-
ware and software standby modes. If the overtemp lim-
its are adjusted while in standby mode, the digital
comparator checks the new values and puts the OVERT
pin in the correct state based on the last valid ADC con-
version. The last valid ADC conversion may include a
conversion performed using the one-shot command.
Supply-current drain during the 125ms conversion peri-
od is always about 450µA. Slowing down the conversion
rate reduces the average supply current (see
Typical
Operating Characteristics ). Between conversions, the
instantaneous supply current is about 25µA due to the
current consumed by the conversion rate timer. In
standby mode, supply current drops to about 3µA. At
very low supply voltages (under the power-on-reset
threshold), the supply current is higher due to the
address pin bias currents. It can be as high as 100µA,
depending on ADD0 and ADD1 settings.
SMBus Digital Interface
From a software perspective, the MAX1619 appears as a
set of byte-wide registers that contain temperature data,
alarm threshold values, or control bits. A standard
SMBus 2-wire serial interface is used to read tempera-
ture data and write control bits and alarm threshold data.
Each A/D channel within the device responds to the
same SMBus slave address for normal reads and writes.
The MAX1619 employs four standard SMBus protocols:
Write Byte, Read Byte, Send Byte, and Receive Byte
(Figure 3). The shorter Receive Byte protocol allows
quicker transfers, provided that the correct data register
was previously selected by a Read Byte instruction. Use
caution with the shorter protocols in multi-master sys-
MAX1619
Remote/Local Temperature Sensor with Dual-
Alarm Outputs and SMBus Serial Interface
10 ______________________________________________________________________________________
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:
equivalent 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 S COMMAND
Slave Address:
equivalent 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 S 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
Figure 3. SMBus Protocols