DS1615 Datasheet, PDF (8/24 Pages) Dallas Semiconductor – Temperature Recorder

DS1615
THERMAL SENSOR
The key to temperature monitoring in the DS1615 is an integrated thermal sensor. The thermal sensor
can measure temperature from -40°C to +85°C in 0.5°C increments (Fahrenheit equivalent is -40°F to
+183.2°F in 0.9°F increments). The thermal sensor provides an accuracy of ±2°C.
The format of temperature data is defined such that the temperature value is maintained in a single byte of
data. Table 1 illustrates the format of the temperature data byte format. The values of T[7..0] range from
00000000b (for -40°C) to 11111010b (for 85°C). Each increment in the value of T[7..0] represents an
increase in temperature of 0.5°C. The following simple formula can be used to translate the temperature
data byte value into degrees Celsius:
°C = 0.5(T[7..0]) - 40
TEMPERATURE DATA BYTE FORMAT Table 1
MSb
LSb
T7
T6
T5
T4
T3
T2
T1
T0
When a datalog mission has been initiated, the DS1615 provides temperature recording at regular
intervals. However, the device also allows for immediate temperature sensing upon a users command
when the device is not currently on a datalog mission. This is accomplished by issuing the Read
Temperature command to the DS1615 over the serial interface.
The most recently recorded temperature value is written to the Current Temperature register, regardless of
whether that value was recorded from a datalog mission or from the issuance of the Read Temperature
command. The status of the contents of this register is provided by the Temperature Ready (TR) bit in
the Status register. If TR is a logic 1, the data is valid. If TR is a logic 0, the data may not be reliable.
During a datalog mission, the TR bit is cleared to a logic 0 when a temperature conversion has been
initiated and is set to a logic 1 upon the completion of the conversion. Likewise, the TR bit is cleared
immediately after the Read Temperature command is issued and is set to a logic 1 upon the completion of
the conversion.
DATA LOGGING
When the DS1615 datalogging function is enabled, the device is said to be on a datalog mission until the
data-logging is stopped.
During a datalog mission, temperature samples are successively written to the Temperature Datalog
memory pages. These memory pages are located at addresses 1000h to 17FFh. The first sample is
written to address location 1000h. The second sample is written to address location 1001h. Likewise, the
address is incremented with each additional data sample. A total of 2048 registers have been reserved for
datalog data.
A datalog mission can be initiated via two different methods; by a host instruction over the serial
interface or by a pushbutton input. When the SE bit in the Control register is cleared to a logic 0, the start
function of the ST pin is disabled and writing any non-zero value to the Sample Rate register will start a
mission. When the SE bit is set to a logic 1, the pushbutton method of starting a mission is enabled.
Under this mode of operation, the DS1615 will begin a datalog mission when a non-zero value has been
written to the Sample Rate register and then the ST pin has been held low for at least 0.5 seconds.
The sample rate during a datalog mission is equal to the value written to the Sample Rate register
multiplied by one minute. Writing a 0 to the MIP bit in the Status register completes the mission.
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