Rainbow Electronics MAX6681 - Manual (Page 13)

still exists, they are reasserted at the end of the next
conversion. If the MAX6680/MAX6681 are operating in
the comparator mode, bits 2–6 of the Status register
are cleared only after the local and/or remote tempera-
tures return within the set limits.
The bits indicating OVTI and OVTE are cleared only
when the condition no longer exists. Reading the status
byte does not clear the OVERT output or fault bits. One
way to eliminate the fault condition is for the measured
temperature to drop below the temperature threshold
minus the hysteresis value. Another way to eliminate
the fault condition is by writing new values for the
RWOI, RWOE, or HYST registers so that a fault condi-
tion is no longer present.
The MAX6680/MAX6681 incorporate collision avoid-
ance so that completely asynchronous operation is
allowed between SMBus operations and temperature
conversions.
When autoconverting, if the T HIGH and T LOW limits are
close together, it is possible for both high-temp and
low-temp status bits to be set, depending on the
amount of time between status read operations. In
these circumstances, it is best not to rely on the status
bits to indicate reversals in long-term temperature
changes. Instead use a current temperature reading to
establish the trend direction.
Hardware/Software Reset
The MAX6680/MAX6681 reset at power-on if pin 7 is
taken high, or by software reset through bit 1 of the
Configuration register. When reset occurs, all registers
go to default values, and the SMBus address pins are
sampled.
Conversion Rate Byte
The Conversion Rate register (Table 8) programs the
time interval between conversions in free-running
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
______________________________________________________________________________________ 13
REGISTER ADDRESS POR STATE FUNCTION
RLTS 00h
0000
at 0°C
Read Internal Temperature
RRTE 01h
0000
(0°C)
Read External Temperature
RSL 02h 0000 0000 Read Status Register
RCL/WCL 03h/09h 0010 0000 Read/Write Configuration Byte
RCRA/WCRA 04h/0A 0000 0010 Read/Write Conversion Rate Byte
RIH/WIH 05h/0Bh
0111 1111
(+127°C)
Read/Write Internal ALERT High Limit
RIL/WIL 06h/0Ch
1100 1001
( -55°C)
Read/Write Internal ALERT Low Limit
REH/WEH 07h/0Dh
0100 0110
(+127°C)
Read/Write External ALERT High Limit
REL/WEL 08h/0Eh
1100 1001
(-55°C)
Read/Write External ALERT Low Limit
OSHT 0Fh 0000 One Shot
REET 10h 0000 0000 Read External Extended Temperature
RWOH 11h 0000 0000 Read/Write External Offset High Byte
RWOL 12h 0000 0000 Read/Write External Offset Low Byte
RWOE 19h See Table 4 Read/Write External OVERT Limit
RWOI 20h See Table 4 Read/Write Internal OVERT Limit
HYST 21h
0000 0110
(+6°C)
OVERT Hysteresis
RDID FEh 0100 1101 Read Manufacturer ID
RDRV Ff 0000 0001 Read Device Revision
Table 5. Command-Byte Register Bit Assignments