DS1721U Datasheet, PDF (6/17 Pages) Maxim Integrated Products – 2-Wire Digital Thermometer and Thermostat

DS1721
R0, R1 = Thermometer Resolution Bits. Table 3 below defines the resolution of the digital thermometer,
based on the settings of these two bits. There is a direct tradeoff between resolution and conversion time,
as depicted in the DC Electrical Characteristics: Digital Thermometer table. The designer has read/write
access to R0 and R1, and the default state is R0="1" and R1="1" (12-bit conversions).
THERMOMETER RESOLUTION CONFIGURATION Table 3
THERMOMETER
R1
R0
RESOLUTION
0
0
9-BIT
0
1
10-BIT
1
0
11-BIT
1
1
12-BIT
MAX
CONVERSION
TIME
93.75ms
187.5ms
375ms
750ms
X = Undefined. These bits are used internally by the DS1721.
DONE = Temperature Conversion Status Bit. "1" = conversion complete and "0" = conversion in
progress. The DONE bit is read-only, and the power-up state is "1". In the continuous conversion mode,
DONE = "0".
Thermostat Setpoints Programming
The thermostat registers (TH and TL) define the setpoints for operation of the TCOM output. The
respective register can be accessed over the 2-wire bus via the Access TH (A1h) or Access TL (A2h)
commands. Reading from or writing to the respective register is controlled by the state of the R/ W bit in
the 2-wire control byte (See “2-Wire Serial Data Bus” section).
The format of the TH and TL registers is a 12-bit 2’s complement representation of the temperature in °C.
The user can program the number of bits (9, 10, 11, or 12) for each TH and TL that correspond to the
thermometer resolution configuration chosen. If the 9-bit mode is chosen, for example, the 3 least
significant bits of TH and TL will be ignored by the thermostat comparator. The format for both TH and
TL is shown in Figure 4. The power-up default of TH is 80°C and that for TL is 75°C.
TEMPERATURE/DATA RELATIONSHIPS Figure 4
S
2⁶
2⁵
2⁴
2³
2²
MSb
(UNIT = °C)
2^-1
2^-2
2^-3
2^-4
0
0
2¹
2⁰
MSB
LSb
0
0
LSB
TEMP
+80°C
+75°C
+10.125°C
+0.5°C
+0°C
-0.5°C
-10.125°C
-25.0625°C
-55°C
DIGITAL OUTPUT
(Binary)
0101 0000 0000 0000
0100 1011 0000 0000
0000 1010 0010 0000
0000 0000 1000 0000
0000 0000 0000 0000
1111 1111 1000 0000
1111 0101 1110 0000
1110 0110 1111 0000
1100 1001 0000 0000
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DIGITAL OUTPUT
(Hex)
5000h
4B00h
0A20h
0080h
0000h
FF80h
F5E0h
E6F0h
C900h