DS1621 Datasheet, PDF (4/16 Pages) Dallas Semiconductor – Digital Thermometer and Thermostat

DS1621
Table 2. TEMPERATURE/DATA RELATIONSHIPS
TEMPERATURE
DIGITAL OUTPUT
(Binary)
+125°C
01111101 00000000
+25°C
00011001 00000000
+½°C
00000000 10000000
+0°C
00000000 00000000
-½°C
11111111 10000000
-25°C
11100111 00000000
-55°C
11001001 00000000
DIGITAL OUTPUT
(Hex)
7D00h
1900h
0080h
0000h
FF80h
E700h
C900h
Since data is transmitted over the 2-wire bus MSB first, temperature data may be written to/read from the
DS1621 as either a single byte (with temperature resolution of 1°C) or as two bytes. The second byte
would contain the value of the least significant (0.5°C) bit of the temperature reading as shown in Table
1. Note that the remaining 7 bits of this byte are set to all "0"s.
Temperature is represented in the DS1621 in terms of a ½°C LSB, yielding the following 9-bit format:
Figure 2. TEMPERATURE, TH, and TL FORMAT
MSB
1 1100 11 1
LSB
0 0 00 0 00 0
T = -25°C
Higher resolutions may be obtained by reading the temperature and truncating the 0.5°C bit (the LSB)
from the read value. This value is TEMP_READ. A Read Counter command should be issued to yield the
COUNT_REMAIN value. The Read Slope command should then be issued to obtain the
COUNT_PER_C value. The higher resolution temperature may be then be calculated by the user using
the following:
TEMPERATURE=TEMP_READ-0.25 + ^{(COUNT _ PER _ C - COUNT _ REMAIN )}
COUNT _ PER _ C
The DS1621 always powers up in a low power idle state, and the Start Convert T command must be used
to initiate conversions.
The DS1621 can be programmed to perform continuous consecutive conversions (continuous-conversion
mode) or to perform single conversions on command (one-shot mode). The conversion mode is
programmed through the 1SHOT bit in the configuration register as explained in the Operation and
Control section of this datasheet. In continuous conversion mode, the DS1621 begins continuous
conversions after a Start Convert T command is issued. Consecutive conversions continue to be
performed until a Stop Convert T command is issued, at which time the device goes into a low-power idle
state. Continuous conversions can be restarted at any time using the Start Convert T command.
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