DS1721U+T&R【PDF 5/17 页】IC THERMOMETER/STAT DIG HP 8USOP

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DS1721

5 of 17

The active state for the totem-pole output is programmable by the user. The power-up default of the

DS1721 has TH=80癈, TL=75癈, and the output state active high. Refer to the OPERATION-

Programming section for instructions in adjusting the thermostat setpoints and T

COM

active state.

THERMOSTAT OUTPUT OPERATION Figure 2

OPERATION-Programming

There are two areas of interest in programming the DS1721: the Configuration/Status register and the

thermostat setpoints. All programming is done via the 2-wire interface using the protocols discussed in

the Command Set section.

Configuration/Status Register Programming

The configuration/status register is accessed via the Access Config (ACh) function command. Writing to

or reading from the register is determined by the R/

W bit of the 2-wire control byte (See 2-wire Serial

Data Bus section). Data is read from or written to the configuration register MSb first. The format of the

below along with the power-up state of the bit and its ability to be read or written to. The entire register is

volatile and will always power-up in the default state. Therefore, it is recommended that the user issue

any configuration programming commands immediately after power is cycled, before any other

commands are issued.

CONFIGURATION/STATUS REGISTER Figure 3

DONE

POL

1SHOT

MSb

LSb

1SHOT = Temperature Conversion Mode. If 1SHOT is "1", the DS1721 will perform and store one

temperature conversion upon reception of the Start Convert T (51h) command. If 1SHOT is "0", the

DS1721 will continuously perform temperature conversions and store the last completed result in the

Thermometer Register. The user has read/write access to the bit and the power-up default state is "0"

(continuous mode).

POL = TCOM Polarity Bit. If POL is "1", the active state of the TCOM output will be high. A "0" stored

in this location sets the thermostat output to an active low state. The user has read/write access to the

POL bit, and the power-up default state is "1" (active high).

U = Undefined. This bit is used internally by the DS1721. It will be a "0" at power-up and will change to

a "1" once the Start Convert T [51h] command is issued. This is a Dont Care on a write; i.e. The

DS1721 will ignore writes to this location.

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