DS1721U+T&R【PDF 6/17 页】IC THERMOMETER/STAT DIG HP 8USOP

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DS1721

6 of 17

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

RESOLUTION

MAX

CONVERSION

TIME

9-BIT

93.75ms

10-BIT

187.5ms

11-BIT

375ms

12-BIT

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 2s complement representation of the temperature in 癈.

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癈 and that for TL is 75癈.

TEMPERATURE/DATA RELATIONSHIPS Figure 4

MSB

MSb

(UNIT = 癈)

LSb

-1

-2

-3

-4

LSB

TEMP

DIGITAL OUTPUT

(Binary)

DIGITAL OUTPUT

(Hex)

+80癈

0101 0000 0000 0000

5000h

+75癈

0100 1011 0000 0000

4B00h

+10.125癈

0000 1010 0010 0000

0A20h

+0.5癈

0000 0000 1000 0000

0080h

+0癈

0000 0000 0000 0000

0000h

-0.5癈

1111 1111 1000 0000

FF80h

-10.125癈

1111 0101 1110 0000

F5E0h

-25.0625癈

1110 0110 1111 0000

E6F0h

-55癈

1100 1001 0000 0000

C900h

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