DS1624 Datasheet, PDF (5/16 Pages) Dallas Semiconductor – Digital Thermometer and Memory

DS1624
three least significant bits of the slave address. The last bit of the control byte (R/ W ) defines the
operation to be performed. When set to a “1”, a read operation is selected, when set to a “0”, a write
operation is selected. Following the START condition the DS1624 monitors the SDA bus checking the
device type identifier being transmitted. Upon receiving the 1001 code and appropriate device select bits,
the slave device outputs an acknowledge signal on the SDA line.
2-WIRE SERIAL COMMUNICATION WITH DS1624 Figure 3
OPERATION-MEASURING TEMPERATURE
A block diagram of the DS1624 is shown in Figure 1. The DS1624 measures temperatures through the
use of an on–board proprietary temperature measurement technique. A block diagram of the temperature
measurement circuitry is shown in Figure 4.
The DS1624 measures temperature by counting the number of clock cycles that an oscillator with a low
temperature coefficient goes through during a gate period determined by a high temperature coefficient
oscillator. The counter is preset with a base count that corresponds to –55°C. If the counter reaches zero
before the gate period is over the temperature register, which is also preset to the –55 °C value, is
incremented indicating that the temperature is higher than –55 °C.
At the same time, the counter is preset with a value determined by the slope accumulator circuitry. This
circuitry is needed to compensate for the parabolic behavior of the oscillators over temperature. The
counter is then clocked again until it reaches zero. If the gate period is still not finished, then this process
repeats.
The slope accumulator is used to compensate for the nonlinear behavior of the oscillators over
temperature, yielding a high resolution temperature measurement. This is done by changing the number
of counts necessary for the counter to go through for each incremental degree in temperature. To obtain
the desired resolution, both the value of the counter and the number of counts per °C (the value of the
slope accumulator) at a given temperature must be known.
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