DS1621

Table 2. TEMPERATURE/DATA RELATIONSHIPS

TEMPERATURE

DIGITAL OUTPUT

(Binary)

DIGITAL OUTPUT

(Hex)

+125°C

01111101 00000000

7D00h

+25°C

00011001 00000000

1900h

+½°C

00000000 10000000

0080h

+0°C

00000000 00000000

0000h

-½°C

11111111 10000000

FF80h

-25°C

11100111 00000000

E700h

-55°C

11001001 00000000

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

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 +

C

PER

COUNT

REMAIN

COUNT

C

PER

COUNT

_

_

)

_

_

_

(

−

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.

1

1

1

0

0

1

1

1

0

0

0

0

0

0

0

0

MSB

LSB

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