DS1721

6 of 16

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

R1

R0

THERMOMETER

RESOLUTION

MAX

CONVERSION

TIME

0

0

9-BIT

0.15s

0

1

10-BIT

0.3s

1

0

11-BIT

0.6s

1

1

12-BIT

1.2s

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)

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

S2

6

2

5

2

4

2

3

2

2

2

1

2

0

MSB

MSb

(UNIT = °C)

LSb

2

-1

2

-2

2

-3

2

-4

0

000

LSB

TEMP

DIGITAL OUTPUT

(Binary)

DIGITAL OUTPUT

(Hex)

+80°C

0101 0000 0000 0000

5000h

+75°C

0100 1011 0000 0000

4B00h

+10.125°C

0000 1010 0010 0000

0A20h

+0.5°C

0000 0000 1000 0000

0080h

+0°C

0000 0000 0000 0000

0000h

-0.5°C

1111 1111 1000 0000

FF80h

-10.125°C

1111 0101 1110 0000

F5E0h

-25.0625°C

1110 0110 1111 0000

E6F0h

-55°C

1100 1001 0000 0000

C900h