Rainbow Electronics MAX6659 - Manual (Page 13)

MAX6657/MAX6658/MAX6659
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Status Byte Functions
The status byte (Table 6) indicates which (if any) tem-
perature thresholds have been exceeded. This byte also
indicates whether the ADC is converting and if there is
an open-circuit fault detected with the external sense
junction. After POR, the normal state of the MSB is 1 and
all the other flag bits are 0, assuming no alert or
overtemperature conditions are present. Bits 2 through
6 of the Status register are cleared by any successful
read of the Status register, unless the fault persists. The
ALERT output follows the status flag bit. Both are
cleared when successfully read, but if the condition still
exists, they reassert at the end of the next conversion.
The bits indicating OVERT1 (bits 0 and 1) are cleared
only when the condition no longer exists. Reading the
status byte does not clear the
OVERT1 outputs 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 OVERT1 threshold or hysteresis so that a fault con-
dition is no longer present. Note that the status byte
does not provide status of
OVERT2.
The MAX6657/MAX6658/MAX6659 incorporate collision
avoidance 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’s 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 circum-
stances, it is best not to rely on the status bits to indi-
cate reversals in long-term temperature changes.
Instead, use a current temperature reading to establish
the trend direction.
Conversion Rate Byte
The Conversion Rate register (Table 7) programs the
time interval between conversions in free-running
autonomous mode (
RUN/STOP = 0). This variable rate
BIT NAME
POR
STATE
FUNCTION
7
(MSB)
MASK1 0 Masks ALERT interrupts if a 1.
6 RUN/STOP 0
Standby mode control bit; if a
1, standby mode is initiated.
5 SPNP 1
Set to 1 when the remote
sensor is a substrate or
common collector PNP. Set to 0
when the remote sensor is a
diode-connected discrete
transistor.
4 to 0 RFU 0 Reserved
Table 5. Configuration-Byte Bit
Assignments
BIT NAME POR STATE FUNCTION (INTEL’S DEFINITION)
7 (MSB) BUSY 1 A/D is busy converting when high.
6 LHIGH 0
Internal high-temperature alarm has tripped when high; cleared by POR or readout of
the Status register if the fault condition no longer exists.
5 LLOW 0
Internal low-temperature alarm has tripped when high; cleared by POR or readout of
the Status register if the fault condition no longer exists.
4 RHIGH 0
External high-temperature alarm has tripped when high; cleared by POR or readout of
the Status register if the fault condition no longer exists.
3 RLOW 0
External low-temperature alarm has tripped when high; cleared by POR or readout of
the Status register if the fault condition no longer exists.
2 OPEN 0
A high indicates an external diode open; cleared by POR or readout of the Status
register if the fault condition no longer exists.
1 EOT1 0
A high indicates the external junction temperature exceeds the external OVERT1
threshold.
0 IOT1 0
A high indicates the internal junction temperature exceeds the internal OVERT1
threshold.
Table 6. Status Register Bit Assignments
±1°C, SMBus-Compatible Remote/Local Temperature
Sensors with Overtemperature Alarms