Rainbow Electronics MAX6681 - Manual (Page 10)

MAX6680/MAX6681
To ensure valid extended data, read extended resolu-
tion temperature data using one of the following
approaches:
1) Put the MAX6680/MAX6681 into standby mode by
setting bit 6 of the Configuration register to 1. Initiate
a one-shot conversion using Send Byte command
0Fh. When this conversion is complete, read the
contents of the temperature data registers.
2) If the MAX6680/MAX6681 are in run mode, read the
Status register. If a conversion is in progress, the
BUSY bit is set to 1. Wait for the conversion to com-
plete as indicated by the BUSY bit being set to zero,
then read the temperature data registers.
Diode Fault Alarm
There is a continuity fault detector at DXP that detects
an open circuit between DXP and DXN, or a DXP short
to V
CC , GND, or DXN. If an open or short circuit exists,
the External Temperature register is loaded with 1000
0000. Additionally, if the fault is an open circuit, bit 2
(OPEN) of the Status byte is set to 1 and the ALERT
condition is activated at the end of the conversion.
Immediately after power-on reset, the Status register
indicates that no fault is present until the end of the first
conversion.
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 out-
put is asserted.
The POR state of both ALERT T HIGH registers is 0111
1111 or +127°C and the POR state of T LOW registers is
1100 1001 or -55°C.
Two additional registers, RWOE and RWOI, store
remote and local alarm threshold data information cor-
responding to the OVERT output (see the
OVERT
Overtemperature Alarm section).
ALERT
The ALERT output operates in two modes—the typical
interrupt mode and comparator mode. The INT_SEL
input determines the mode. When INT_SEL is connect-
ed to V
CC high, using a weak pullup resistor, or left
floating, the ALERT functions in the interrupt mode.
ALERT
Interrupt Mode
An ALERT interrupt occurs when the internal or external
temperature reading exceeds a high or low tempera-
ture limit (user programmed) or when the remote diode
is disconnected (for continuity fault detection). The
ALERT interrupt output signal is latched and can be
cleared only by either reading the Status register or by
successfully responding to an Alert Response address.
In both cases, the alert is cleared even if the fault con-
dition still exists, but is reasserted at the end of the next
conversion. The interrupt does not halt automatic con-
versions. The interrupt output pin is open drain so that
multiple devices can share a common interrupt line.
The interrupt rate never exceeds the conversion rate.
Comparator Mode
Connecting INT_SEL to ground operates the ALERT
output in comparator mode. In the comparator mode,
whenever the temperature of the remote or local temp
sensor goes outside the limits set by T
HIGH
or T
LOW
,
the ALERT output becomes inactive after the tempera-
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
10 ______________________________________________________________________________________
TEMP ( °C)
LEGACY MODE
DIGITAL OUTPUT
EXTENDED
RANGE
DIGITAL OUTPUT
127.00 0111 1111 0111 1111
25 0001 1001 0001 1001
1 0000 0001 0000 0001
0.00 0000 0000 0000 0000
-1 0000 0000 1111 1111
-25 0000 0000 1110 0111
-64 0000 0000 1000 0000
Diode Fault
(Short or
Open)
1000 0000 1000 0000
Table 2. Data Format (Two’s Complement)
FRACTIONAL
TEMPERATURE
CONTENTS OF
EXTENDED REGISTER
0.000 000X XXXX
0.125 001X XXXX
0.250 010X XXXX
0.375 011X XXXX
0.500 100X XXXX
0.625 101X XXXX
0.750 110X XXXX
0.875 111X XXXX
Table 3. Extended Resolution Register
Note: Extended mode applies only for conversion rates of 4Hz
and slower.