Rainbow Electronics DS1616 - Manual (Page 11)

DS1616
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occurred. If rollover has occurred, the user needs to determine how many times rollover occurred in
determining the sample time for any particular data sample.
As a safety measure, the DS1616 has been designed such that the end user cannot write to the Datalog
Memory. This prevents the falsification of datalog data by writing values to datalog registers.
DATA HISTOGRAM
While on a datalog mission, the DS1616 also records a histogram of the temperature and/or ADC
Channel 1 data. The temperature histogram is provided by a series of 63 2-byte “data bins” that are
located in the Temperature Histogram memory pages (addresses 0800h to 087Fh). Each bin consists of a
16-bit binary counter that is incremented each time an acquired temperature value falls into the range of
the bin. The least significant byte of each bin is stored at the lower address. Bin 0 begins at memory
address 0800h, bin 1 at 0802h, and so on up to 087Ch for bin 62. See Figure 2d for temperature
histogram address map.
Likewise, the ADC Channel 1Data histogram is provided by a series of 64 2-byte “data bins” that are
located in the ADC Data Histogram memory pages (addresses 0880h to 08FFh). Each data bin represents
four ADC codes (32mV/bin). For example, bin 0 counts the frequency of ADC codes from 00-03h. Bin
1 counts the frequency of ADC codes from 04-07h, and so on. See Figure 2e for ADC Data histogram
address map.
After a temperature and/or ADC conversion is completed, the number of the bin to be updated is
determined by dropping the two least significant bits of the binary data value. For example, bin 0 of the
temperature histogram 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 2 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.
ALARM LOGGING
For some applications it may be essential to record exactly when a data sample exceeds a predefined
tolerance band and for how long the violation remained. The Thermal Sensor (CS1) and ADC Channel 1
(CS2) are equipped with the alarm logging feature. The ADC Channels 2 & 3 do not have the logging
feature, but they still have the alarm feature and the ability to trigger an interrupt. If an out of tolerance
condition occurs on channels 2 or 3, the time and duration can be calculated from the Memory if the
memory has not rolled over since the alarm.
A tolerance band is specified by means of the Temperature Alarm registers (addresses 000Bh and 000Ch)
and the ADC Data Alarm [1-3] registers (addresses 0024h to 0029h). See figure 2b for more details on
the memory mapping. One can set a high and a low threshold. As long as the data samples stay within
the tolerance bands (i.e., are higher than the low threshold and lower than the high threshold), the DS1616
will not record any alarm.
If the temperature violates the temperature band, the DS1616 will generate an alarm and set either the
Temperature-High Flag (THF) or the Temperature-Low Flag (TLF) in the Status 1 register (address
0014h). In addition, the device generates a time stamp of when the alarm occurred and records the