DS1615 Datasheet, PDF (10/24 Pages) Dallas Semiconductor – Temperature Recorder

DS1615
After a temperature conversion is completed, the number of the bin to be updated is determined by
dropping the two least significant bits of the binary temperature value. Thus, bin 0 will be updated with
every temperature reading from -40°C to -38.5°C. In the same way, bin 1 is associated with the range of -
38°C to -36.5°C. Bin 62, finally, counts temperature values in the range of +84°C to 85.0°C. Since the
device will not generate temperature values higher than 85.0°C, bin 62 covers only three temperature
values. The memory for a potential 64 th bin exists, but will always read 0s.
Since each data bin contains two bytes, a total of 65,535 samples can be accumulated. If more samples
are measured, the data bin will remain at the maximum value. In other words, the data bin value will not
roll-over in the event of an overrun.
TEMPERATURE ALARM LOGGING
For some applications it may be essential to record exactly when a temperature sample exceeds a
predefined tolerance band and for how long the temperature violation remained.
A tolerance band is specified by means of the Temperature Alarm registers, addresses 000Bh and 000Ch.
The user can set a high and a low temperature threshold. As long as the temperature samples stay within
this tolerance band (i.e., are higher than the low threshold and lower than the high threshold), the DS1615
will not record any temperature alarm. If the temperature violates the temperature band, the DS1615 will
generate an alarm and set either the Temperature High Flag (THF) or the Temperature Low Flag (TLF) in
the Status register (address 0014h). In addition, the device generates a time stamp of when the alarm
occurred and records the duration of the alarming condition. The INT pin will be asserted by a high
temperature alarm if the Temperature High Interrupt Enable (THIE) is set and will be asserted by a low
temperature alarm if the Temperature Low Interrupt Enable (TLIE) is set.
The device stores a time stamp of a violating condition by copying contents of the three-byte Current
Samples Counter when the alarm occurred. The least significant byte is stored at the lower address. One
address higher than each time stamp, the DS1615 maintains a one byte duration counter that stores the
number of times the temperature was found to be beyond the threshold. If this counter has reached its
limit after 255 consecutive temperature readings and the temperature has not yet returned to a level within
the tolerance band, the device will issue another time stamp at the next higher address and open another
counter to record the duration. If the temperature returns to normal before the counter has reached its
limit, the duration counter of the particular time stamp will not increment any further. Should the
temperature again cross this threshold, another time stamp will be recorded and its associated counter will
increment with each temperature reading outside the tolerance band. This algorithm is implemented for
the low as well as for the high temperature threshold.
Time stamps and durations where the temperature violates the low temperature threshold are stored in the
address range 0220h to 024Fh (48 bytes). The memory address range 0250h to 027Fh (48 bytes) is
reserved for time stamps and duration where the temperature exceeds the high temperature threshold.
This allocation allows to record 24 individual alarm events and periods (12 periods for too hot and 12 for
too cold). The date and time of each of these periods can be determined from the Start Time Stamp and
the time distance between each temperature reading. Figure 2c illustrates the Alarm Time Stamps and
Durations register.
INSPEC AND OUTSPEC PINS
Two special output pins, INSPEC and OUTSPEC , are intended to output the status of the DS1615. More
specifically, these pins can be used to control the illumination of LEDs. For example, the INSPEC pin can
be used to pulse a green LED and the OUTSPEC pin can be used to pulse a red LED. When the end user
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