DS1615
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Upon initiation of datalog mission by either method, the DS1615 will do two things:
1.
The INSPEC and OUTSPEC pins will generate four low pulses simultaneously.
2.
The Mission-in-Progress (MIP) bit in the Status register is set to a one.
The time at which the first datalog sample is measured is dependent upon the value in the Start Delay
registers. The two Start Delay registers provide a method for the end user to program a delay before
sampling commences. The delay is roughly equal to the value in the Start Delay registers times one
minute. For example, if the Start Delay registers contain a value of ten, then the device will begin
recording data approximately ten minutes after it received either the pushbutton start signal or start
instruction. The Start Delay registers are located at addresses 0012h and 0013h, with register 0012h
being the LSB and register 0013h being the MSB. The Start Delay register decrements every time the
Seconds register rolls over from 59 to 00. When this Start Delay register contains a 00, the first datalog
sample will be taken when the seconds register rolls over from 59 to 00.
The user has two options for dealing with the potential occurrence of a data overrun (i.e., more than 2048
total data samples). The first option is to enable the rollover feature of the DS1615. This is accomplished
by setting the Rollover bit (bit 3 of the Control register) to 1. When the Rollover feature is enabled, new
data is written over previous data, starting with address 0000h. For example, if the Datalog memory has
been completely filled (i.e., 2048 data samples have been recorded) the next data sample will be written
to address location 1000h and the address pointer will be incremented with each successive data sample.
The second option for dealing with data overrun is to stop the recording of data after the datalog memory
has been completely used. In other words, the DS1615 will stop recording data values after 2048 data
samples. This feature is enabled by disabling the Rollover feature. (bit 3 of the Control register set to 0).
It should be noted that during a datalog mission, a time stamp for the first sample is recorded, but is not
included for each subsequent sample. However, the time of acquisition for any data sample is easily
determined by considering the start time, the sample rate, the value in the Current Sample Counter, and
the address of the particular data sample in the datalog memory. If no rollover has occurred in the datalog
memory, the sample time associated with any particular data point can be calculated by multiplying the
address of the data by the sample rate and adding that to the stored start time value. If the rollover feature
has been enabled, the user can determine if rollover has occurred by reading the value in the Current
Samples register. This register counts the total number of samples that have been acquired. If this value
is greater than 07FFh (decimal 2047) then the user knows that rollover has 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 DS1615 has been designed such that the end user cannot write to the
Temperature Datalog Memory. This prevents the falsification of data-log data by writing values to
datalog registers.
DATA HISTOGRAM
While on a datalog mission, the DS1615 also records a histogram of the recorded temperature data. The
histo-gram is provided by a series of 63 two-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.
