DS1720 查看數據表（PDF） - Dallas Semiconductor -> Maxim Integrated

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DS1720

Econo – Digital Thermometer and Thermostat

Dallas Semiconductor -> Maxim Integrated 

TEMPERATURE MEASURING CIRCUITRY Figure 2

SLOPE ACCUMULATOR

PRESET

DS1720

COMPARE

LOW TEMPERATURE

COEFFICIENT OSCILLATOR

COUNTER

PRESET

SET/CLEAR

LSB

INC

=0

TEMPERATURE REGISTER

HIGH TEMPERATURE

COEFFICIENT OSCILLATOR

COUNTER

=0 STOP

This calculation is done inside the DS1720 to provide

0.5°C resolution. The temperature reading is provided

in a 9–bit, two’s complement reading by issuing a READ

TEMPERATURE command. Table 1 describes the

exact relationship of output data to measured tempera-

ture. The data is transmitted serially through the 3–wire

serial interface, LSB first. The DS1720 can measure

temperature over the range of –55°C to +125°C in 0.5°C

increments. For Fahrenheit usage, a lookup table or con-

version factor must be used.

TEMPERATURE/DATA RELATIONSHIPS

Table 1

TEMP

DIGITAL

OUTPUT

(Binary)

DIGITAL

OUTPUT

(Hex)

+85°C

0 10101010

00AA

+25°C

0 00110010

0032h

+1/2°C

+0°C

0 00000001

0 00000000

0001h

0000h

–1/2°C

–25°C

1 11111111

1 11001110

01FFh

01CEh

Since data is transmitted over the 3–wire bus LSB first,

temperature data can be written to/read from the

DS1720 as either a 9–bit word (taking RST low after the

9th (MSB) bit), or as two transfers of 8–bit words, with

the most significant 7 bits being ignored or set to zero,

as illustrated in Table 1. After the MSB, the DS1720 will

output 0s.

Note that temperature is represented in the DS1720 in

terms of a 1/2°C LSB, yielding the following 9–bit format:

MSB

X X X XX XX 1

LSB

1 1 0 01 11 0

T = –25°C

Higher resolutions may be obtained by reading the tem-

perature, and truncating the 0.5°C bit (the LSB) from the

read value. This value is TEMP_READ. The value left in

the counter may then be read by issuing a READ

COUNTER command. This value is the count remain-

ing (COUNT_REMAIN) after the gate period has

ceased. By loading the value of the slope accumulator

into the count register (using the READ SLOPE com-

mand), this value may then be read, yielding the number

of counts per degree C (COUNT_PER_C) at that tem-

perature. The actual temperature may be then be calcu-

lated by the user using the following:

(COUNT_PER_C – COUNT_REMAIN)

TEMPERATURE = TEMP_READ – 0.25 )

COUNT_PER_C

030598 3/12

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