DS18S20 datasheet(4/27 Pages) DALLAS

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DS18S20

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For situations where the bus master does not know whether the DS18S20s on the bus are parasite

powered or supplied with external VDD, a provision is made in the DS18S20 to signal the power supply

scheme used. The bus master can determine if any DS18S20s are on the bus which require the strong

pullup by sending a Skip ROM protocol, then issuing the read power supply command.

After this

command is issued, the master then issues read time slots. The DS18S20 will send back “0” on the

1-Wire bus if it is parasite powered; it will send back a “1” if it is powered from the VDD pin. If the

master receives a “0,” it knows that it must supply the strong pullup on the DQ line during temperature

conversions. See “Memory Command Functions” section for more detail on this command protocol.

STRONG PULL-UP FOR SUPPLYING DS18S20 DURING TEMPERATURE

CONVERSION Figure 2

USING VDD TO SUPPLY TEMPERATURE CONVERSION CURRENT Figure 3

+3V - +5V

DS18S20

+3V - +5V

4.7k

GND

VDD

I/O

µµµµP

+3V - +5V

4.7k

µµµµP

DS18S20

GND

VDD

I/O

TO OTHER

1-WIRE DEVICES

EXTERNAL +3V - +5V

SUPPLY

DS18S20 Datasheet(PDF) 4 Page - Dallas Semiconductor