DS18S20-PAR 1-Wire Parasite-Power Digital Thermometer www.maxim-ic.com FEATURES PIN ASSIGNMENT Unique 1-Wire interface requires only one port pin for communication DALLAS Derives power from data line (parasite 18S20P power)does not need a local power supply 1 23 Multi-drop capability simplifies distributed temperature sensing applications Requires no external components 0.5 C accuracy from 10C to +85C Measures temperatures from 55C to +100C (67F to +212F) 9-bit thermometer resolution Converts temperature in 750 ms (max.) Userdefinable non-volatile temperature alarm settings Alarm search command identifies and addresses devices whose temperature is 1 23 outside of programmed limits (temperature alarm condition) (BOTTOM VIEW) Ideal for use in remote sensing applications TO-92 (e.g., temperature probes) that do not have a local power source (DS18S20-PAR) PIN DESCRIPTION GND - Ground DQ - Data In/Out NC - No Connect DESCRIPTION The DS18S20-PAR digital thermometer provides 9bit centigrade temperature measurements and has an alarm function with nonvolatile user-programmable upper and lower trigger points. The DS18S20-PAR does not need an external power supply because it derives power directly from the data line (parasite power). The DS18S20-PAR communicates over a 1-Wire bus, which by definition requires only one data line (and ground) for communication with a central microprocessor. It has an operating temperature range of 55C to +100C and is accurate to 0.5 C over a range of 10C to +85C. Each DS18S20-PAR has a unique 64-bit identification code, which allows multiple DS18S20-PARs to function on the same 1wire bus thus, it is simple to use one microprocessor to control many DS18S20-PARs distributed over a large area. Applications that can benefit from this feature include HVAC environmental controls, temperature monitoring systems inside buildings, equipment or machinery, and process monitoring and control systems. 1-Wire is a registered trademark of Dallas Semiconductor. 1 of 20 111803 GND DQ NCDS18S20-PAR DETAILED PIN DESCRIPTIONS Table 1 PIN SYMBOL DESCRIPTION 1 GND Ground. 2DQ Data Input/Output pin. Open-drain 1-Wire interface pin. Also provides power to the device when used in parasite power mode (see Parasite Power section.) 3NC No Connect. Doesnt connect to internal circuit. OVERVIEW The DS18S20-PAR 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 via a 3-state or open-drain port (the DQ pin in the case of the DS18S20-PAR). In this bus system, the microprocessor (the master device) identifies and addresses devices on the bus using each devices 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 datasheet. An important feature of the DS18S20-PAR is its ability to operate without an external power supply. Power is instead supplied through the 1-Wire pullup resistor via the DQ pin when the bus is high. The high bus signal also charges an internal capacitor (C ), which then supplies power to the device when the PP bus is low. This method of deriving power from the 1-Wire bus is referred to as parasite power. Figure 1 shows a block diagram of the DS18S20-PAR, and pin descriptions are given in Table 1. The 64-bit ROM stores the devices 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 lower alarm trigger registers (T and T ). The T and T H L H L registers are nonvolatile (EEPROM), so they will retain their data when the device is powered down. DS18S20-PAR BLOCK DIAGRAM Figure 1 V PU PARASITE POWER 4.7K MEMORY CONTROL DS18S20-PAR CIRCUIT LOGIC DQ TEMPERATURE SENSOR 64-BIT ROM INTERNAL V DD AND 1-wire PORT ALARM HIGH TRIGGER (T ) H SCRATCHPAD C REGISTER (EEPROM) PP ALARM LOW TRIGGER (T ) L REGISTER (EEPROM) GND 8-BIT CRC GENERATOR 2 of 20