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FEATURES

· Unique 1-Wire

interface requires only one

port pin for communication

· Derives power from data line (“parasite

power”)—does not need a local power supply

· Multi-drop capability simplifies distributed

temperature sensing applications

· Requires no external components

· ±0.5°C accuracy from –10°C to +85°C

· Measures temperatures from –55°C to

+100°C (–67°F to +212°F)

· 9-bit thermometer resolution

· Converts temperature in 750 ms (max.)

· User–definable non-volatile temperature

alarm settings

· Alarm search command identifies and

addresses devices whose temperature is

outside of programmed limits (temperature

alarm condition)

· Ideal for use in remote sensing applications

(e.g., temperature probes) that do not have a

local power source

PIN ASSIGNMENT

PIN DESCRIPTION

GND - Ground

DQ - Data In/Out

NC - No Connect

DESCRIPTION

The DS18S20-PAR digital thermometer provides 9–bit 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 –55°C to +100°C and is accurate to ±0.5°C over a range of –10°C to +85°C.

Each DS18S20-PAR has a unique 64-bit identification code, which allows multiple DS18S20-PARs to

function on the same 1–wire 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.

DS18S20-PAR

1-Wire Parasite-Powe

Digital Thermomete

www.maxim

ic.com

TO-92

(

DS18S20-PAR

)

(

BOTTOM VIEW

)

DALLAS

18S20P

GND

1-Wire is a registered trademark of Dallas Semiconductor.

Summary of content (20 pages)

PAGE 1
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 Derives power from data line (“parasite power”)—does not need a local power supply Multi-drop capability simplifies distributed temperature sensing applications Requires no external components ±0.
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DS18S20-PAR DETAILED PIN DESCRIPTIONS Table 1 PIN 1 2 SYMBOL GND DQ 3 NC DESCRIPTION Ground. 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.) No Connect. Doesn’t connect to internal circuit. OVERVIEW The DS18S20-PAR uses Dallas’ exclusive 1-Wire bus protocol that implements bus communication using one control signal.
PAGE 3
DS18S20-PAR PARASITE POWER The DS18S20-PAR’s parasite power circuit allows the DS18S20-PAR to operate without a local external power supply. This ability is especially useful for applications that require remote temperature sensing or that are very space constrained. Figure 1 shows the DS18S20-PAR’s parasite-power control circuitry, which “steals” power from the 1-Wire bus via the DQ pin when the bus is high.
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DS18S20-PAR 16 (10h). After reading the scratchpad, the TEMP_READ value is obtained by truncating the 0.5°C bit (bit 0) from the temperature data (see Figure 3). The extended resolution temperature can then be calculated using the following equation: TEMPERATURE = TEMP _ READ - 0.
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DS18S20-PAR so the master can determine exactly which DS18S20-PARs have experienced an alarm condition. If an alarm condition exists and the TH or TL settings have changed, another temperature conversion should be done to validate the alarm condition. 64-BIT LASERED ROM CODE Each DS18S20-PAR contains a unique 64–bit code (see Figure 5) stored in ROM. The least significant 8 bits of the ROM code contain the DS18S20-PAR’s 1–wire family code: 10h. The next 48 bits contain a unique serial number.
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DS18S20-PAR DS18S20-PAR MEMORY MAP Figure 6 SCRATCHPAD (Power-up State) byte 0 Temperature LSB (AAh) (85°C) byte 1 Temperature MSB (00h) byte 2 TH Register or User Byte 1* EEPROM TH Register or User Byte 1 byte 3 TL Register or User Byte 2* TL Register or User Byte 2 byte 4 Reserved (FFh) byte 5 Reserved (FFh) byte 6 COUNT REMAIN (0Ch) byte 7 COUNT PER °C (10h) byte 8 CRC* *Power-up state depends on value(s) stored in EEPROM CRC GENERATION CRC bytes are provided as part of the DS18S20-PAR’s 64-bit
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DS18S20-PAR 1-WIRE BUS SYSTEM The 1-Wire bus system uses a single bus master to control one or more slave devices. The DS18S20PAR is always a slave. When there is only one slave on the bus, the system is referred to as a “singledrop” system; the system is “multi-drop” if there are multiple slaves on the bus. All data and commands are transmitted least significant bit first over the 1-Wire bus.
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DS18S20-PAR It is very important to follow the transaction sequence every time the DS18S20-PAR is accessed, as the DS18S20-PAR will not respond if any steps in the sequence are missing or out of order. Exceptions to this rule are the Search ROM [F0h] and Alarm Search [ECh] commands. After issuing either of these ROM commands, the master must return to Step 1 in the sequence. INITIALIZATION All transactions on the 1-Wire bus begin with an initialization sequence.
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DS18S20-PAR read from the device without sending its 64–bit ROM code. This sequence will cause a data collision on the bus if there is more than one slave since multiple devices will attempt to transmit data simultaneously. ALARM SEARCH [ECh] The operation of this command is identical to the operation of the Search ROM command except that only slaves with a set alarm flag will respond.
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DS18S20-PAR DS18S20-PAR FUNCTION COMMAND SET Table 4 Command Convert T Read Scratchpad Write Scratchpad Copy Scratchpad 2 Recall E 1-Wire Bus Activity Description Protocol After Command is Issued TEMPERATURE CONVERSION COMMANDS Initiates temperature 44h None conversion. MEMORY COMMANDS Reads the entire scratchpad BEh DS18S20-PAR transmits up including the CRC byte. to 9 data bytes to master. Writes data into scratchpad 4Eh Master transmits 2 data bytes 2 and 3 (TH and TL). bytes to DS18S20-PAR.
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DS18S20-PAR ROM COMMANDS FLOW CHART Figure 9 Initialization Sequence MASTER TX RESET PULSE DS18S20-PAR TX PRESENCE PULSE MASTER TX ROM COMMAND 33h READ ROM COMMAND Y N 55h MATCH ROM COMMAND F0h SEARCH ROM COMMAND N Y N Y ECh ALARM SEARCH COMMAND N Y Y MASTER TX BIT 0 DS18S20-PAR TX BIT 0 DS18S20-PAR TX BIT 0 DS18S20-PAR TX BIT 0 DS18S20-PAR TX BIT 0 MASTER TX BIT 0 MASTER TX BIT 0 DS18S20-PAR TX FAMILY CODE 1 BYTE N BIT 0 MATCH? DS18S20-PAR TX SERIAL NUMBER 6 BYTES N BIT 0 MATCH?
PAGE 12
DS18S20-PAR DS18S20-PAR FUNCTION COMMANDS FLOW CHART Figure 10 44h CONVERT TEMPERATURE ? MASTER TX FUNCTION COMMAND 48h COPY SCRATCHPAD ? N Y Y MASTER ENABLES STRONG PULL-UP ON DQ MASTER ENABLES STRONG PULLUP ON DQ DATA COPIED FROM SCRATCHPAD TO EEPROM DS18S20-PAR CONVERTS TEMPERATURE MASTER DISABLES STRONG PULLUP MASTER DISABLES STRONG PULLUP N B8h RECALL E2 ? BEh READ SCRATCHPAD ? N Y N Y 4Eh WRITE SCRATCHPAD ? Y MASTER TX TH BYTE TO SCRATCHPAD MASTER RX DATA BYTE FROM SCRATCHPAD MAS
PAGE 13
DS18S20-PAR 1-WIRE SIGNALING The DS18S20-PAR uses a strict 1-Wire communication protocol to insure data integrity. Several signal types are defined by this protocol: reset pulse, presence pulse, write 0, write 1, read 0, and read 1. All of these signals, with the exception of the presence pulse, are initiated by the bus master.
PAGE 14
DS18S20-PAR The DS18S20-PAR samples the 1-Wire bus during a window that lasts from 15 ms to 60 ms after the master initiates the write time slot. If the bus is high during the sampling window, a 1 is written to the DS18S20-PAR. If the line is low, a 0 is written to the DS18S20-PAR.
PAGE 15
DS18S20-PAR release the bus by the end of the time slot, and the bus will be pulled back to its high idle state by the pullup resister. Output data from the DS18S20-PAR is valid for 15 ms after the falling edge that initiated the read time slot. Therefore, the master must release the bus and then sample the bus state within 15 ms from the start of the slot. Figure 13 illustrates that the sum of TINIT, TRC, and TSAMPLE must be less than 15 ms for a read time slot.
PAGE 16
DS18S20-PAR DS18S20-PAR OPERATION EXAMPLE 1 In this example there is only one DS18S20-PAR on the bus. The master writes to the TH and TL registers in the DS18S20-PAR scratchpad and then reads the scratchpad and recalculates the CRC to verify the data. The master then copies the scratchpad contents to EEPROM.
PAGE 17
DS18S20-PAR DS18S20-PAR OPERATION EXAMPLE 2 In this example there are multiple DS18S20-PARs on the bus. The bus master initiates a temperature conversion in a specific DS18S20-PAR and then reads its scratchpad and recalculates the CRC to verify the data. MASTER MODE TX RX TX TX TX TX TX RX TX TX TX RX DATA (LSB FIRST) Reset Presence 55h 64-bit ROM code 44h DQ line held high by strong pullup Reset Presence 55h 64-bit ROM code BEh 9 data bytes COMMENTS Master issues reset pulse.
PAGE 18
DS18S20-PAR ABSOLUTE MAXIMUM RATINGS* Voltage on any pin relative to ground Operating temperature Storage temperature Soldering temperature –0.5V to +6.0V –55°C to +100°C –55°C to +125°C See J-STD-020A Specification *These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
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DS18S20-PAR AC ELECTRICAL CHARACTERISTICS (-55°C to +100°C; VPU=3.0V to 5.
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DS18S20-PAR TIMING DIAGRAMS Figure 16 20 of 20