DS1825 Programmable Resolution 1-Wire Digital Thermometer With 4-Bit ID

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OVERVIEW

Figure 1 shows a block diagram of the DS1825, and pin descriptions are given in Table 1. The 64-bit ROM stores

the device’s unique serial code. The scratchpad memory contains the 2-byte temperature register that stores the

digital output from the temperature sensor. In addition, the scratchpad provides access to the 1-byte upper and

user to set the resolution of the temperature-to-digital conversion to 9, 10, 11, or 12 bits. It is also used for the hard-

they will retain data when the device is powered down.

The DS1825 uses Dallas’ exclusive 1-Wire bus protocol that implements bus communication using one control

signal. The control line requires a weak pullup resistor since all devices are linked to the bus through a 3-state or

open-drain port (the DQ pin in the case of the DS1825). In this bus system, the microprocessor (the master device)

identifies and addresses devices on the bus using each device’s unique 64-bit code. Because each device has a

unique code, the number of devices that can be addressed on one bus is virtually unlimited. The 1-Wire bus

protocol, including detailed explanations of the commands and “time slots,” is covered in the 1-Wire BUS SYSTEM

section of this data sheet.

Another feature of the DS1825 is the ability to operate without an external power supply. Power is instead supplied

through the 1-Wire pullup resistor through the DQ pin when the bus is high. The high bus signal also charges an

power from the 1-Wire bus is referred to as “parasite power.” As an alternative, the DS1825 can also be powered

Figure 1. DS1825 BLOCK DIAGRAM

Power

Supply

Sense

64-Bit ROM

And

1-wire Port

S

C

R

A

T

C

P

A

D

16-bit Temp Reg

8-bit Config. Reg

8-bit CRC Gen

Memory

Control Logic

GND

DQ

AD0-AD3

4.7k

Parasite

Power

Circuit

Cpp

Address Pin

Input Latch