If the remote channel is shorted (DXP to DXN or DXP to
GND), the ADC reads 0000 0000 so as not to trip either
the T
HIGH
or T
LOW
alarms at their POR settings. In
applications that are never subjected to 0°C in normal
operation, a 0000 0000 result can be checked to indi-
cate a fault condition in which DXP is accidentally short
circuited. Similarly, if DXP is short circuited to V
CC
, the
ADC reads +127°C for both remote and local channels,
and the ALERT and OVERT outputs are activated.
AALLEERRTT
Interrupts
The ALERT interrupt output signal is latched and can
only be cleared by reading the Alert Response address.
Interrupts are generated in response to T
HIGH
and T
LOW
comparisons and when the remote diode is disconnect-
ed (for continuity fault detection). The interrupt does not
halt automatic conversions; new temperature data con-
tinues to be available over the SMBus interface after
ALERT is asserted. The interrupt output pin is open-drain
so that devices can share a common interrupt line. The
interrupt rate can never exceed the conversion rate.
The interface responds to the SMBus Alert Response
address, an interrupt pointer return-address feature
(see
Alert Response Address
section). Prior to taking
corrective action, always check to ensure that an inter-
rupt is valid by reading the current temperature.
To prevent reoccurring interrupts, the MAX1619 asserts
ALERT only once per crossing of a given temperature
threshold. To enable a new interrupt, the value in the
limit register that triggered the interrupt must be rewrit-
ten. Note that other interrupt conditions can be caused
by crossing the opposite temperature threshold, or a
diode fault can still cause an interrupt.
Example: the remote temperature reading crosses
T
HIGH
, activating ALERT. The host responds to the
interrupt and reads the Alert Response address, clear-
ing the interrupt. The system may also read the status
byte at this time. The condition that caused the interrupt
persists, but no new ALERT interrupt is issued. Finally,
the host writes a new value to T
HIGH
. This enables the
device to generate a new T
HIGH
interrupt if the alert
condition still exists.
Alert Response Address
The SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that lack
the complex, expensive logic needed to be a bus master.
Upon receiving an ALERT interrupt signal, the host mas-
ter can broadcast a Receive Byte transmission to the
Alert Response slave address (0001 100). Then any slave
device that generated an interrupt attempts to identify
itself by putting its own address on the bus (Table 3).
The Alert Response can activate several different slave
devices simultaneously, similar to the I
2
C™ General
Call. If more than one slave attempts to respond, bus
arbitration rules apply, and the device with the lower
address code wins. The losing device does not gener-
ate an acknowledge and continues to hold the ALERT
line low until serviced (implies that the host interrupt
input is level-sensitive). Successful reading of the alert
response address clears the interrupt latch.
Command Byte Functions
The 8-bit command byte register (Table 4) is the master
index that points to the other registers within the
MAX1619. The register’s POR state is 0000 0001 so
that a Receive Byte transmission (a protocol that lacks
the command byte) that occurs immediately after POR
returns the current remote temperature data.
The one-shot command immediately forces a new conver-
sion cycle to begin. In software standby mode
(RUN/STOP bit = high), a new conversion is begun, after
which the device returns to standby mode. If a conversion
is in progress when a one-shot command is received, the
command is ignored. If a one-shot command is received
in auto-convert mode (RUN/STOP bit = low) between con-
versions, a new conversion begins, the conversion rate
timer is reset, and the next automatic conversion takes
place after a full delay elapses.
Configuration Byte Functions
The configuration byte register (Table 5) is used to
mask (disable) interrupts, to put the device in software
standby mode, to change the polarity of the OVERT
output, and to enable the write-once protection. The
lowest two bits are internally set to zeros, making them
“don’t care” bits. This register’s contents can be read
back over the serial interface.
MAX1619
Remote/Local Temperature Sensor with Dual-
Alarm Outputs and SMBus Serial Interface
12 ______________________________________________________________________________________
I
2
C is a trademark of Philips Corp.
Table 3. Read Format for Alert Response
Address (0001100)
ADD66
Provide the current MAX1619
slave address
FUNCTION
ADD55
ADD44
ADD33
ADD22
ADD11
ADD7
7
(MSB)
1
0
(LSB)
Logic 1
BIT NAME
