DS1722S【PDF 6/14 页】IC THERMOMETER DIG 3-WIRE 8-SOIC

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DS1722

6 of 14

CONFIGURATION/STATUS REGISTER Figure 2

1SHOT

MSb

LSb

1SHOT = One-shot temperature conversion bit. If the SD bit is "1", (continuous temperature

conversions are not taking place), a "1" written to the 1SHOT bit will cause the DS1722 to perform one

temperature conversion and store the results in the temperature register at addresses 01h (LSB) and 02h

(MSB). The bit will clear itself to "0" upon completion of the temperature conversion. The user has

read/write access to the 1SHOT bit, although writes to this bit will be ignored if the SD bit is a "0",

(continuous conversion mode). The power-up default of the one-shot bit is "0".

R0, R1, R2 = Thermometer resolution bits. Table 5 below defines the resolution of the digital

thermometer, based on the settings of these 3 bits. There is a direct tradeoff between resolution and

conversion time, as depicted in the AC Electrical Characteristics. The user has read/write access to the

R2, R1 and R0 bits and the power-up default state is R2="0", R1="0", and R0="1" (9-bit conversions).

THERMOMETER RESOLUTION CONFIGURATION Table 5

R2 R1 R0

Thermometer Resolution

Max Conversion Time

8-bit

0.075s

9-bit

0.15s

10-bit

0.3s

11-bit

0.6s

12-bit

1.2s

x=Dont care.

SD = Shutdown bit. If SD is "0", the DS1722 will continuously perform temperature conversions and

store the last completed result in the temperature register. If SD is changed to a "1", the conversion in

progress will be completed and stored and then the device will revert to a low-power shutdown mode.

The communication port remains active. The user has read/write access to the SD bit and the power-up

default is "1" (shutdown mode).

SERIAL INTERFACE

The DS1722 offers the flexibility to choose between two serial interface modes. The DS1722 can

communicate with the SPI interface or with a standard 3-wire interface. The interface method used is

determined by the SERMODE pin. When this pin is connected to V

DDD

SPI communication is selected.

When this pin is connected to ground, standard 3-wire communication is selected.

SERIAL PERIPHERAL INTERFACE (SPI)

The serial peripheral interface (SPI) is a synchronous bus for address and data transfer. The SPI mode of

serial communication is selected by tying the SERMODE pin to V

DDD

. Four pins are used for the SPI.

The four pins are the SDO (Serial Data Out), SDI (Serial Data In), CE (Chip Enable), and SCLK (Serial

Clock). The DS1722 is the slave device in an SPI application, with the microcontroller being the master.

The SDI and SDO pins are the serial data input and output pins for the DS1722, respectively. The CE

input is used to initiate and terminate a data transfer. The SCLK pin is used to synchronize data

movement between the master (microcontroller) and the slave (DS1722) devices.

The shift clock (SCLK), which is generated by the microcontroller, is active only when CE is high and

during address and data transfer to any device on the SPI bus. The inactive clock polarity is

programmable in some microcontrollers. The DS1722 offers an important feature in that the level of the

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