General Description DS18B20

The DS18B20 digital thermometer provides 9-bit, 12-bit Celsius temperature measurement and has an alarm function with the non-volatile top of the user and a lower trigger point. DS18B20 communicates more than 1-Wire bus which by definition only requires one data path (and ground) for communication with the center of the microprocessor. 

In addition, it can originate the DS18B20 power directly from the data path ("parasitic power"), eliminating the need for an external power supply. Each DS18B20 has a unique 64-bit serial code that allows multiple DS18B20s to function on 1-Wire with the same bus. 

So, it's easy to use one multiple DS18B20 control microprocessor that is distributed over a large area. Applications that can take advantage of this feature include HVAC environment control, system temperature monitoring in buildings, equipment or machinery, and system monitoring and control processes.

Benefits and Features DS18B20

The Unique 1-Wire® Interface Requires Only One Port Pin for Communication. Reduce Component Counts with Integrated Temperature Sensors and EEPROM. Measuring temperatures from -55 ° C to + 125 ° C (-67 ° F to + 257 ° F). Programmable Resolution from 9 Bit to 12 Bit. External Components Not Required. 

Parasitic Power Mode Only Requires 2 Pins for Operation (DQ and GND). Simplifies the Temperature Sensation of Application Distributed with Multidrop Capabilities. Nonvolatile (NV) Flexible User Alarm Settings with Identifying Alarm Search Commands Devices with Programmed Out-of-Temperature Temperature. Available in SO 8-Pin (150 miles), 8-Pin ┬ÁSOP, and 3-Pin TO-92 Package.


Overview DS18B20

Figure 3 shows a DS18B20 block diagram, and a pin description is given in the Description Pin table. 64-bit ROM stores the device's unique serial code. The scratchpad memory contains a 2-byte temperature register that stores digital output from the sensor temperature. In addition, the Scratchpad provides access to registers that trigger up and down 1 byte alarms (TH and TL) and 1-byte configuration registers. 

The register configuration allows users to set the temperature-to-digital conversion resolution to 9, 10, 11 or 12 bits. TH, TL, and non-volatile configuration registers (EEPROM), so they will store data when the device is turned off. DS18B20 uses the exclusive 1-wire bus protocol Maxim that implements bus communication using one signal control. 

The control line requires a weak pullup resistor because all devices are linked to the bus through 3-state or open-drain ports (pin DQ in the case of DS18B20). In this bus system, the microprocessor (master device) identifies and handles devices on the bus using the unique 64-bit code of each device. Because each device has a unique code, the number of devices can be overcome on an almost unlimited bus in DS18B20. 

The 1-wire bus protocol, including a detailed description of the command and "time slot," is included in the Bus 1-Wire Section system. Instead, the power is supplied through a 1-wire pullup resistor via DQ pin when the bus is high. The high bus signal also fills internal capacitors (CPP), which then supplies power to the device when the bus is low. This method obtains power from a 1-wire bus called "parasitic power." 

Alternatively, the DS18B20 may also be powered by an external supply on VDD. Operation - Measuring Temperature The core functionality of DS18B20 is direct-digital temperature sensor. The temperature resolution of the sensor can be user configured up to 9, 10, 11, or 12 bits, according to increases of 0.5 ° C, 0.25 ° C, 0.125 ° C, and 0.0625 ° C, respectively. The default resolution of the power-up is 12-bit. 

DS18B20 power in low power stationary state. To start temperature measurement and A-to-D conversion, the master must issue the T Conversion Command [44j]. After conversion, the results of thermal data are stored in 2-byte temperature registers in scratchpad memory and DS18B20 returns to memory idle. 

If the DS18B20 is powered by an external supply, the master can issue a "read time slot" (see 1-Wire System Bus Section) after the Convert T and DS18B20 commands will respond by transmitting 0 when the conversion temperature is in progress and 1 when the conversion is done. 

If the DS18B20 is empowered with parasitic power, this notification technique cannot be used since then the bus must be pulled high with strong withdrawals during the conversion of all temperatures. The bus requirements for parasitic strength are explained in detail in the DS18B20 Section.