DS18B20数据手册_引脚图_参数

General Description

The DS18B20 digital thermometer provides 9-bit to 12-bit Celsius temperature measurements and has an alarm function with nonvolatile user-programmable upper and lower trigger points. The DS18B20 communicates over a 1-Wire bus that by definition requires only one data line (and ground) for communication with a central micro-processor. In addition, the DS18B20 can derive power directly from the data line (“parasite power”), eliminating the need for an external power supply.

Each DS18B20 has a unique 64-bit serial code, which allows multiple DS18B20s to function on the same 1-Wire bus. Thus, it is simple to use one microprocessor to control many DS18B20s 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.

Applications

●Thermostatic Controls ●Industrial Systems ●Consumer Products ●Thermometers

●Thermally Sensitive Systems

Benefits and Features

●Unique 1-Wire ? Interface Requires Only One Port

Pin for Communication

●Reduce Component Count with Integrated

Temperature Sensor and EEPROM

? Measures Temperatures from -55°C to +125°C (-67°F to +257°F)

? ±0.5°C Accuracy from -10°C to +85°C

? Programmable Resolution from 9 Bits to 12 Bits ? No External Components Required ●Parasitic Power Mode Requires Only 2 Pins for

Operation (DQ and GND) ●Simplifies Distributed Temperature-Sensing

Applications with Multidrop Capability

? Each Device Has a Unique 64-Bit Serial Code Stored in On-Board ROM ●Flexible User-Definable Nonvolatile (NV) Alarm Settings

with Alarm Search Command Identifies Devices with T emperatures Outside Programmed Limits ●Available in 8-Pin SO (150 mils), 8-Pin μSOP , and

3-Pin TO-92 Packages

19-7487; Rev 4; 1/15

1-Wire is a registered trademark of Maxim Integrated Products, Inc.

1-Wire Digital Thermometer

Voltage Range on Any Pin Relative to Ground ....-0.5V to +6.0V Operating Temperature Range .........................-55°C to +125°C

Storage Temperature Range ............................-55°C to +125°C Solder Temperature ...............................Refer to the IPC/JEDEC

J-STD-020 Specification.

(-55°C to +125°C; V DD = 3.0V to 5.5V)

Note 1: All voltages are referenced to ground.

Note 2: The Pullup Supply Voltage specification assumes that the pullup device is ideal, and therefore the high level of the

pullup is equal to V PU . In order to meet the V IH spec of the DS18B20, the actual supply rail for the strong pullup transis-tor must include margin for the voltage drop across the transistor when it is turned on; thus: V PU_ACTUAL = V PU_IDEAL + V TRANSISTOR .

Note 3: See typical performance curve in Figure 1.

Note 4: Logic-low voltages are specified at a sink current of 4mA.

Note 5: To guarantee a presence pulse under low voltage parasite power conditions, V ILMAX may have to be reduced to as low as

0.5V.

Note 6: Logic-high voltages are specified at a source current of 1mA.

Note 7: Standby current specified up to +70°C. Standby current typically is 3μA at +125°C.

Note 8: To minimize I DDS , DQ should be within the following ranges: GND ≤ DQ ≤ GND + 0.3V or V DD – 0.3V ≤ DQ ≤ V DD .Note 9: Active current refers to supply current during active temperature conversions or EEPROM writes.Note 10: DQ line is high (“high-Z” state).

Note 11: Drift data is based on a 1000-hour stress test at +125°C with V DD = 5.5V.

PARAMETER

SYMBOL CONDITIONS

MIN TYP

MAX UNITS Supply Voltage V DD Local power (Note 1)+3.0+5.5V Pullup Supply Voltage V PU Parasite power (Notes 1, 2)+3.0+5.5V Local power +3.0

V DD Thermometer Error t ERR -10°C to +85°C (Note 3)

±0.5°C -55°C to +125°C ±2Input Logic-Low V IL (Notes 1, 4, 5)-0.3+0.8V Input Logic-High V IH Local power (Notes 1,6)+2.2The lower of 5.5 or V DD + 0.3

V Parasite power +3.0Sink Current I L V I/O = 0.4V 4.0

mA Standby Current I DDS (Notes 7, 8)7501000nA Active Current I DD V DD = 5V (Note 9)1 1.5

mA DQ Input Current I DQ

(Note 10)5μA Drift

(Note 11)

±0.2

°C

1-Wire Digital Thermometer

Absolute Maximum Ratings

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.

DC Electrical Characteristics

(-55°C to +125°C; V DD = 3.0V to 5.5V)

(-55°C to +125°C; V DD = 3.0V to 5.5V)

Note 12: See the timing diagrams in Figure 2.

Note 13: Under parasite power, if t RSTL > 960μs, a power-on reset can occur.

Figure 1. Typical Performance Curve

PARAMETER

SYMBOL CONDITIONS

MIN

TYP MAX UNITS NV Write Cycle Time t WR 2

10

ms EEPROM Writes N EEWR -55°C to +55°C 50k writes EEPROM Data Retention

t EEDR

-55°C to +55°C

10

years

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX UNITS

Temperature Conversion Time

t CONV

9-bit resolution

(Note 12)

93.75ms 10-bit resolution 187.511-bit resolution 37512-bit resolution

750Time to Strong Pullup On t SPON Start convert T command issued 10μs Time Slot t SLOT (Note 12)60120

μs Recovery Time t REC (Note 12)1μs Write 0 Low Time t LOW0(Note 12)60120μs Write 1 Low Time t LOW1(Note 12)1

15μs Read Data Valid t RDV (Note 12)15

μs Reset Time High t RSTH (Note 12)480μs Reset Time Low t RSTL (Notes 12, 13)480μs Presence-Detect High t PDHIGH (Note 12)1560μs Presence-Detect Low t PDLOW (Note 12)

60

240μs Capacitance

C IN/OUT

25

pF

1-Wire Digital Thermometer

AC Electrical Characteristics–NV Memory

AC Electrical Characteristics

Figure 2. Timing Diagrams

PIN

NAME FUNCTION

SO μSOP TO-921, 2, 6, 7, 82, 3, 5, 6, 7—N.C.No Connection

383V DD Optional V DD . V DD must be grounded for operation in parasite power mode.412DQ Data Input/Output. Open-drain 1-Wire interface pin. Also provides power to the

device when used in parasite power mode (see the Powering the DS18B20 section.) 5

4

1

GND

Ground

1-Wire Digital Thermometer

Pin Description

Overview

Figure 3 shows a block diagram of the DS18B20, and pin descriptions are given in the Pin Description table. 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 lower alarm trigger registers (T H and T L ) and the 1-byte configuration register. The configura-tion register allows the user to set the resolution of the temperature-to-digital conversion to 9, 10, 11, or 12 bits. The T H , T L , and configuration registers are nonvolatile (EEPROM), so they will retain data when the device is powered down.

The DS18B20 uses Maxim’s exclusive 1-Wire bus proto-col 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 DS18B20). 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.

Another feature of the DS18B20 is the ability to oper-ate 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 internal capacitor (C PP ), which then supplies power to the device when the bus is low. This method of deriving power from the 1-Wire bus is referred to as “para-site power.” As an alternative, the DS18B20 may also be powered by an external supply on V DD .

Operation—Measuring Temperature

The core functionality of the DS18B20 is its direct-to-digital temperature sensor. The resolution of the tempera-ture sensor is user-configurable to 9, 10, 11, or 12 bits, corresponding to increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C, respectively. The default resolution at power-up is 12-bit. The DS18B20 powers up in a low-power idle state. To initiate a temperature measurement and A-to-D conversion, the master must issue a Convert T [44h] command. Following the conversion, the resulting thermal data is stored in the 2-byte temperature register in the scratchpad memory and the DS18B20 returns to its idle state. If the DS18B20 is powered by an external sup-ply, the master can issue “read time slots” (see the 1-Wire Bus System section) after the Convert T command and the DS18B20 will respond by transmitting 0 while the tem-perature conversion is in progress and 1 when the con-version is done. If the DS18B20 is powered with parasite power, this notification technique cannot be used since the bus must be pulled high by a strong pullup during the entire temperature conversion. The bus requirements for parasite power are explained in detail in the Powering the DS18B20 section.

Figure 3. DS18B20 Block Diagram

1-Wire Digital Thermometer

The DS18B20 output temperature data is calibrated in degrees Celsius; for Fahrenheit applications, a lookup table or conversion routine must be used. The tempera-ture data is stored as a 16-bit sign-extended two’s comple-ment number in the temperature register (see Figure 4). The sign bits (S) indicate if the temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. If the DS18B20 is configured for 12-bit resolution, all bits in the temperature register will contain valid data. For 11-bit resolution, bit 0 is undefined. For 10-bit resolution, bits 1 and 0 are undefined, and for 9-bit resolution bits 2, 1, and 0 are undefined. Table 1 gives examples of digital output data and the corresponding temperature reading for 12-bit resolution conversions.

Operation—Alarm Signaling

After the DS18B20 performs a temperature conversion, the temperature value is compared to the user-defined two’s complement alarm trigger values stored in the 1-byte T H and T L registers (see Figure 5). The sign bit (S) indicates if the value is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. The T H and T L registers are nonvolatile (EEPROM) so they will retain data when the device is powered down. T H and T L can be accessed through bytes 2 and 3 of the scratchpad as explained in the Memory section.

Only bits 11 through 4 of the temperature register are used in the T H and T L comparison since T H and T L are 8-bit registers. If the measured temperature is lower than

Figure 4. Temperature Register Format

Figure 5. T H and T L Register Format

Table 1. Temperature/Data Relationship

*The power-on reset value of the temperature register is +85°C.

TEMPERATURE (°C)

DIGITAL OUTPUT

(BINARY)DIGITAL OUTPUT

(HEX)

+1250000 0111 1101 000007D0h +85*0000 0101 0101 00000550h +25.06250000 0001 1001 00010191h +10.1250000 0000 1010 001000A2h +0.50000 0000 0000 10000008h 00000 0000 0000 00000000h -0.51111 1111 1111 1000FFF8h -10.1251111 1111 0101 1110FF5Eh -25.06251111 1110 0110 1111FE6Fh -55

1111 1100 1001 0000

FC90h

BIT 7

BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0LS BYTE 232221202-12-22-32-4BIT 15BIT 14BIT 13BIT 12BIT 11BIT 10BIT 9BIT 8MS BYTE S

S

S

S

S

26

25

24

S = SIGN

BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0S

26

25

24

23

22

21

20

1-Wire Digital Thermometer

or equal to T L or higher than or equal to T H, an alarm con-dition exists and an alarm flag is set inside the DS18B20. This flag is updated after every temperature measure-ment; therefore, if the alarm condition goes away, the flag will be turned off after the next temperature conversion. The master device can check the alarm flag status of all DS18B20s on the bus by issuing an Alarm Search [ECh] command. Any DS18B20s with a set alarm flag will respond to the command, so the master can determine exactly which DS18B20s have experienced an alarm condition. If an alarm condition exists and the T H or T L settings have changed, another temperature conversion should be done to validate the alarm condition. Powering the DS18B20

The DS18B20 can be powered by an external supply on the V DD pin, or it can operate in “parasite power” mode, which allows the DS18B20 to function without a local external supply. Parasite power is very useful for applica-tions that require remote temperature sensing or that are very space constrained. Figure 3 shows the DS18B20’s parasite-power control circuitry, which “steals” power from the 1-Wire bus via the DQ pin when the bus is high. The stolen charge powers the DS18B20 while the bus is high, and some of the charge is stored on the parasite power capacitor (C PP) to provide power when the bus is low. When the DS18B20 is used in parasite power mode, the V DD pin must be connected to ground.

In parasite power mode, the 1-Wire bus and CPP can pro-vide sufficient current to the DS18B20 for most operations as long as the specified timing and voltage requirements are met (see the DC Electrical Characteristics and AC Electrical Characteristics). However, when the DS18B20 is performing temperature conversions or copying data from the scratchpad memory to EEPROM, the operating current can be as high as 1.5mA. This current can cause an unacceptable voltage drop across the weak 1-Wire pullup resistor and is more current than can be supplied by C PP. To assure that the DS18B20 has sufficient supply current, it is necessary to provide a strong pullup on the 1-Wire bus whenever temperature conversions are tak-ing place or data is being copied from the scratchpad to EEPROM. This can be accomplished by using a MOSFET to pull the bus directly to the rail as shown in Figure 6. The 1-Wire bus must be switched to the strong pullup within 10μs (max) after a Convert T [44h] or Copy Scratchpad [48h] command is issued, and the bus must be held high by the pullup for the duration of the conversion (t CONV) or data transfer (t WR = 10ms). No other activity can take place on the 1-Wire bus while the pullup is enabled.

The DS18B20 can also be powered by the conventional method of connecting an external power supply to the V DD pin, as shown in Figure 7. The advantage of this method is that the MOSFET pullup is not required, and the 1-Wire bus is free to carry other traffic during the tem-perature conversion time.

The use of parasite power is not recommended for tem-peratures above +100°C since the DS18B20 may not be able to sustain communications due to the higher leak-age currents that can exist at these temperatures. For applications in which such temperatures are likely, it is strongly recommended that the DS18B20 be powered by an external power supply.

In some situations the bus master may not know whether the DS18B20s on the bus are parasite powered or pow-ered by external supplies. The master needs this informa-tion to determine if the strong bus pullup should be used during temperature conversions. To get this information, the master can issue a Skip ROM [CCh] command fol-lowed by a Read Power Supply [B4h] command followed by a “read time slot”. During the read time slot, parasite powered DS18B20s will pull the bus low, and externally powered DS18B20s will let the bus remain high. If the bus is pulled low, the master knows that it must supply the strong pullup on the 1-Wire bus during temperature conversions.

Figure 6. Supplying the Parasite-Powered DS18B20 During Temperature Conversions Figure 7. Powering the DS18B20 with an External Supply

1-Wire Digital Thermometer

64-BIT Lasered ROM code

Each DS18B20 contains a unique 64–bit code (see Figure 8) stored in ROM. The least significant 8 bits of the ROM code contain the DS18B20’s 1-Wire family code: 28h. The next 48 bits contain a unique serial number. The most significant 8 bits contain a cyclic redundancy check (CRC) byte that is calculated from the first 56 bits of the ROM code. A detailed explanation of the CRC bits is provided in the CRC Generation section. The 64-bit ROM code and associated ROM function control logic allow the DS18B20 to operate as a 1-Wire device using the protocol detailed in the 1-Wire Bus System section.

Memory

The DS18B20’s memory is organized as shown in Figure 9. The memory consists of an SRAM scratchpad with nonvolatile EEPROM storage for the high and low alarm trigger registers (T H and T L ) and configuration register. Note that if the DS18B20 alarm function is not used, the TH and TL registers can serve as general-purpose memory. All memory commands are described in detail in the DS18B20 Function Commands section.

Byte 0 and byte 1 of the scratchpad contain the LSB and the MSB of the temperature register, respectively. These bytes are read-only. Bytes 2 and 3 provide access to TH and TL registers. Byte 4 contains the configuration regis-

ter data, which is explained in detail in the Configuration Register section. Bytes 5, 6, and 7 are reserved for inter-nal use by the device and cannot be overwritten.

Byte 8 of the scratchpad is read-only and contains the CRC code for bytes 0 through 7 of the scratchpad. The DS18B20 generates this CRC using the method described in the CRC Generation section.

Data is written to bytes 2, 3, and 4 of the scratchpad using the Write Scratchpad [4Eh] command; the data must be transmitted to the DS18B20 starting with the least signifi-cant bit of byte 2. To verify data integrity, the scratchpad can be read (using the Read Scratchpad [BEh] command) after the data is written. When reading the scratchpad, data is transferred over the 1-Wire bus starting with the least significant bit of byte 0. To transfer the T H , T L and configuration data from the scratchpad to EEPROM, the master must issue the Copy Scratchpad [48h] command. Data in the EEPROM registers is retained when the device is powered down; at power-up the EEPROM data is reloaded into the corresponding scratchpad locations. Data can also be reloaded from EEPROM to the scratch-pad at any time using the Recall E 2 [B8h] command. The master can issue read time slots following the Recall E 2 command and the DS18B20 will indicate the status of the recall by transmitting 0 while the recall is in progress and 1 when the recall is done.

Figure 8. 64-Bit Lasered ROM Code

Figure 9. DS18B20 Memory Map

8-BIT CRC

48-BIT SERIAL NUMBER

8-BIT FAMILY CODE (28h)

MSB

LSB

MSB

LSB

MSB

LSB

1-Wire Digital Thermometer

Configuration Register

Byte 4 of the scratchpad memory contains the configura-tion register, which is organized as illustrated in Figure 10. The user can set the conversion resolution of the DS18B20 using the R0 and R1 bits in this register as shown in T able 2. The power-up default of these bits is R0 = 1 and R1 = 1 (12-bit resolution). Note that there is a direct tradeoff between resolution and conversion time. Bit 7 and bits 0 to 4 in the configuration register are reserved for internal use by the device and cannot be overwritten.

CRC Generation

CRC bytes are provided as part of the DS18B20’s 64-bit ROM code and in the 9th byte of the scratchpad memory. The ROM code CRC is calculated from the first 56 bits of the ROM code and is contained in the most significant byte of the ROM. The scratchpad CRC is calculated from the data stored in the scratchpad, and therefore it chang-es when the data in the scratchpad changes. The CRCs provide the bus master with a method of data validation when data is read from the DS18B20. To verify that data has been read correctly, the bus master must re-calculate the CRC from the received data and then compare this value to either the ROM code CRC (for ROM reads) or to the scratchpad CRC (for scratchpad reads). If the cal-culated CRC matches the read CRC, the data has been

received error free. The comparison of CRC values and the decision to continue with an operation are determined entirely by the bus master. There is no circuitry inside the DS18B20 that prevents a command sequence from pro-ceeding if the DS18B20 CRC (ROM or scratchpad) does not match the value generated by the bus master.The equivalent polynomial function of the CRC (ROM or scratchpad) is:

CRC = X 8 + X 5 + X 4 + 1

The bus master can re-calculate the CRC and compare it to the CRC values from the DS18B20 using the polyno-mial generator shown in Figure 11. This circuit consists of a shift register and XOR gates, and the shift register bits are initialized to 0. Starting with the least significant bit of the ROM code or the least significant bit of byte 0 in the scratchpad, one bit at a time should shifted into the shift register. After shifting in the 56th bit from the ROM or the most significant bit of byte 7 from the scratchpad, the polynomial generator will contain the recalculated CRC. Next, the 8-bit ROM code or scratchpad CRC from the DS18B20 must be shifted into the circuit. At this point, if the re-calculated CRC was correct, the shift register will contain all 0s. Additional information about the Maxim 1-Wire cyclic redundancy check is available in Application Note 27: Understanding and Using Cyclic Redundancy Checks with Maxim iButton Products .

Figure 10. Configuration Register

Figure 11. CRC Generator

Table 2. Thermometer Resolution Configuration

R1R0RESOLUTION

(BITS)

MAX CONVERSION TIME 009 93.75ms (t CONV /8)0110187.5ms (t CONV /4)1011375ms (t CONV /2)1

1

12

750ms

(t CONV )

BIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 00

R1

R0

1

1

1

1

1

1-Wire Digital Thermometer

1-Wire Bus System

The 1-Wire bus system uses a single bus master to con-trol one or more slave devices. The DS18B20 is always a slave. When there is only one slave on the bus, the sys-tem is referred to as a “single-drop” system; the system is “multidrop” if there are multiple slaves on the bus. All data and commands are transmitted least significant bit first over the 1-Wire bus.

The following discussion of the 1-Wire bus system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing).

Hardware Configuration

The 1-Wire bus has by definition only a single data line. Each device (master or slave) interfaces to the data line via an open-drain or 3-state port. This allows each device to “release” the data line when the device is not transmit-ting data so the bus is available for use by another device. The 1-Wire port of the DS18B20 (the DQ pin) is open drain with an internal circuit equivalent to that shown in Figure 12.

The 1-Wire bus requires an external pullup resistor of approximately 5k?; thus, the idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus MUST be left in the idle state if the transaction is to resume. Infinite recovery time can occur between bits so long as the 1-Wire bus is in the inactive (high) state during the recovery period. If the bus is held low for more than 480μs, all components on the bus will be reset.

Transaction Sequence

The transaction sequence for accessing the DS18B20 is as follows:

Step 1. Initialization

Step 2. ROM Command (followed by any required data

exchange)Step 3. DS18B20 Function Command (followed by any

required data exchange)It is very important to follow this sequence every time the DS18B20 is accessed, as the DS18B20 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 initializa-tion sequence. The initialization sequence consists of a reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the slave(s). The pres-ence pulse lets the bus master know that slave devices (such as the DS18B20) are on the bus and are ready to operate. Timing for the reset and presence pulses is detailed in the 1-Wire Signaling section.

ROM Commands

After the bus master has detected a presence pulse, it can issue a ROM command. These commands operate on the unique 64-bit ROM codes of each slave device and allow the master to single out a specific device if many are present on the 1-Wire bus. These commands also allow the master to determine how many and what types of devices are present on the bus or if any device has experienced an alarm condition. There are five ROM commands, and each command is 8 bits long. The master device must issue an appropriate ROM command before issuing a DS18B20 function command. A flowchart for operation of the ROM commands is shown in Figure 13.

Search Rom [F0h]

When a system is initially powered up, the master must identify the ROM codes of all slave devices on the bus, which allows the master to determine the number of slaves and their device types. The master learns the ROM codes through a process of elimination that requires the master to perform a Search ROM cycle (i.e., Search ROM command followed by data exchange) as many times as necessary to identify all of the slave devices.

Figure 12. Hardware Configuration

1-Wire Digital Thermometer

If there is only one slave on the bus, the simpler Read ROM [33h] command can be used in place of the Search ROM process. For a detailed explanation of the Search ROM procedure, refer to Application Note 937: Book of iButton? Standards. After every Search ROM cycle, the bus master must return to Step 1 (Initialization) in the transaction sequence.

Read Rom [33h]

This command can only be used when there is one slave on the bus. It allows the bus master to read the slave’s 64-bit ROM code without using the Search ROM proce-dure. If this command is used when there is more than one slave present on the bus, a data collision will occur when all the slaves attempt to respond at the same time. Match Rom [55H]

The match ROM command followed by a 64-bit ROM code sequence allows the bus master to address a specific slave device on a multidrop or single-drop bus. Only the slave that exactly matches the 64-bit ROM code sequence will respond to the function command issued by the master; all other slaves on the bus will wait for a reset pulse.

Skip Rom [CCh]

The master can use this command to address all devices on the bus simultaneously without sending out any ROM code information. For example, the master can make all DS18B20s on the bus perform simultaneous temperature conversions by issuing a Skip ROM command followed by a Convert T [44h] command.

Note that the Read Scratchpad [BEh] command can follow the Skip ROM command only if there is a single slave device on the bus. In this case, time is saved by allowing the master to read from the slave without send-ing the device’s 64-bit ROM code. A Skip ROM command followed by a Read Scratchpad command 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. This command allows the master device to determine if any DS18B20s experienced an alarm condition during the most recent temperature conversion. After every Alarm Search cycle (i.e., Alarm Search command followed by data exchange), the bus master must return to Step 1 (Initialization) in the transac-tion sequence. See the Operation—Alarm Signaling sec-tion for an explanation of alarm flag operation.

DS18B20 Function Commands

After the bus master has used a ROM command to address the DS18B20 with which it wishes to communi-cate, the master can issue one of the DS18B20 function commands. These commands allow the master to write to and read from the DS18B20’s scratchpad memory, initiate temperature conversions and determine the power supply mode. The DS18B20 function commands, which are described below, are summarized in Table 3 and illus-trated by the flowchart in Figure 14.

Convert T [44h]

This command initiates a single temperature conversion. Following the conversion, the resulting thermal data is stored in the 2-byte temperature register in the scratch-pad memory and the DS18B20 returns to its low-power idle state. If the device is being used in parasite power mode, within 10μs (max) after this command is issued the master must enable a strong pullup on the 1-Wire bus for the duration of the conversion (t CONV) as described in the Powering the DS18B20 section. If the DS18B20 is powered by an external supply, the master can issue read time slots after the Convert T command and the DS18B20 will respond by transmitting a 0 while the temperature conversion is in progress and a 1 when the conversion is done. In parasite power mode this notification technique cannot be used since the bus is pulled high by the strong pullup during the conversion.

Write Scratchpad [4Eh]

This command allows the master to write 3 bytes of data to the DS18B20’s scratchpad. The first data byte is written into the T H register (byte 2 of the scratchpad), the second byte is written into the T L register (byte 3), and the third byte is written into the configuration register (byte 4). Data must be transmitted least significant bit first. All three bytes MUST be written before the master issues a reset, or the data may be corrupted.

Read Scratchpad [BEh]

This command allows the master to read the contents of the scratchpad. The data transfer starts with the least sig-nificant bit of byte 0 and continues through the scratchpad until the 9th byte (byte 8 – CRC) is read. The master may issue a reset to terminate reading at any time if only part of the scratchpad data is needed.

iButton is a registered trademark of Maxim Integrated Products, Inc.

1-Wire Digital Thermometer

Copy Scratchpad [48h]

This command copies the contents of the scratchpad T H , T L and configuration registers (bytes 2, 3 and 4) to EEPROM. If the device is being used in parasite power mode, within 10μs (max) after this command is issued the master must enable a strong pullup on the 1-Wire bus for at least 10ms as described in the Powering the DS18B20 section.

Recall E 2 [B8h]

This command recalls the alarm trigger values (T H and T L ) and configuration data from EEPROM and places the data in bytes 2, 3, and 4, respectively, in the scratchpad memory. The master device can issue read time slots

following the Recall E 2 command and the DS18B20 will indicate the status of the recall by transmitting 0 while the recall is in progress and 1 when the recall is done. The recall operation happens automatically at power-up, so valid data is available in the scratchpad as soon as power is applied to the device.

Read Power Supply [B4h]

The master device issues this command followed by a read time slot to determine if any DS18B20s on the bus are using parasite power. During the read time slot, para-site powered DS18B20s will pull the bus low, and exter-nally powered DS18B20s will let the bus remain high. See the Powering the DS18B20 section for usage information for this command.

Table 3. DS18B20 Function Command Set

Note 1: For parasite-powered DS18B20s, the master must enable a strong pullup on the 1-Wire bus during temperature conver-sions and copies from the scratchpad to EEPROM. No other bus activity may take place during this time.

Note 2: The master can interrupt the transmission of data at any time by issuing a reset.Note 3: All three bytes must be written before a reset is issued.

COMMAND

DESCRIPTION

PROTOCOL

1-Wire BUS ACTIVITY AFTER

COMMAND IS ISSUED

NOTES

TEMPERATURE CONVERSION COMMANDS

Convert T

Initiates temperature conversion.

44h

DS18B20 transmits conversion status to master (not applicable for parasite-powered DS18B20s).

1

MEMORY COMMANDS

Read

Scratchpad Reads the entire scratchpad including the CRC byte.

BEh DS18B20 transmits up to 9 data bytes to master.

2Write

Scratchpad Writes data into scratchpad bytes 2, 3, and 4 (T H , T L , and configuration registers).4Eh Master transmits 3 data bytes to DS18B20.3Copy

Scratchpad Copies T H , T L , and configuration register data from the scratchpad to EEPROM.48h None

1

Recall E 2Recalls T H , T L , and configuration register data from EEPROM to the scratchpad.B8h DS18B20 transmits recall status to master.

Read Power Supply

Signals DS18B20 power supply mode to the master.

B4h

DS18B20 transmits supply status to master.

1-Wire Digital Thermometer

1-Wire Digital Thermometer

Figure 13. ROM Commands Flowchart

1-Wire Digital Thermometer

Figure 14. DS18B20 Function Commands Flowchart

1-Wire Signaling

The DS18B20 uses a strict 1-Wire communication pro-tocol to ensure data integrity. Several signal types are defined by this protocol: reset pulse, presence pulse, write 0, write 1, read 0, and read 1. The bus master initiates all these signals, with the exception of the presence pulse.

Initialization Procedure—Reset And Presence Pulses

All communication with the DS18B20 begins with an ini-tialization sequence that consists of a reset pulse from the master followed by a presence pulse from the DS18B20. This is illustrated in Figure 15. When the DS18B20 sends the presence pulse in response to the reset, it is indicating to the master that it is on the bus and ready to operate. During the initialization sequence the bus master trans-mits (T X ) the reset pulse by pulling the 1-Wire bus low for a minimum of 480μs. The bus master then releases the bus and goes into receive mode (R X ). When the bus is released, the 5k? pullup resistor pulls the 1-Wire bus high. When the DS18B20 detects this rising edge, it waits 15μs to 60μs and then transmits a presence pulse by pull-ing the 1-Wire bus low for 60μs to 240μs.

Read/Write Time Slots

The bus master writes data to the DS18B20 during write time slots and reads data from the DS18B20 during read time slots. One bit of data is transmitted over the 1-Wire bus per time slot.

Write Time Slots

There are two types of write time slots: “Write 1” time slots and “Write 0” time slots. The bus master uses a Write 1 time slot to write a logic 1 to the DS18B20 and a Write 0 time slot to write a logic 0 to the DS18B20. All write time slots must be a minimum of 60μs in duration with a minimum of a 1μs recovery time between individual write slots. Both types of write time slots are initiated by the master pulling the 1-Wire bus low (see Figure 14).To generate a Write 1 time slot, after pulling the 1-Wire bus low, the bus master must release the 1-Wire bus within 15μs. When the bus is released, the 5k? pullup resistor will pull the bus high. To generate a Write 0 time slot, after pulling the 1-Wire bus low, the bus master must continue to hold the bus low for the duration of the time slot (at least 60μs).

The DS18B20 samples the 1-Wire bus during a window that lasts from 15μs to 60μs after the master initiates the write time slot. If the bus is high during the sampling win-dow, a 1 is written to the DS18B20. If the line is low, a 0 is written to the DS18B20.

Figure 15. Initialization Timing

1-Wire Digital Thermometer

Read Time Slots

The DS18B20 can only transmit data to the master when the master issues read time slots. Therefore, the master must generate read time slots immediately after issuing a Read Scratchpad [BEh] or Read Power Supply [B4h] command, so that the DS18B20 can provide the request-ed data. In addition, the master can generate read time slots after issuing Convert T [44h] or Recall E 2 [B8h] com-mands to find out the status of the operation as explained in the DS18B20 Function Commands section.

All read time slots must be a minimum of 60μs in duration with a minimum of a 1μs recovery time between slots. A read time slot is initiated by the master device pulling the 1-Wire bus low for a minimum of 1μs and then releasing the bus (see Figure 16). After the master initiates the

read time slot, the DS18B20 will begin transmitting a 1 or 0 on bus. The DS18B20 transmits a 1 by leaving the bus high and transmits a 0 by pulling the bus low. When transmitting a 0, the DS18B20 will 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 DS18B20 is valid for 15μs after the falling edge that initiated the read time slot. Therefore, the master must release the bus and then sample the bus state within 15μs from the start of the slot.

Figure 17 illustrates that the sum of T INIT , T RC , and T SAMPLE must be less than 15μs for a read time slot. Figure 18 shows that system timing margin is maximized by keeping T INIT and T RC as short as possible and by locating the master sample time during read time slots towards the end of the 15μs period.

Figure 16. Read/Write Time Slot Timing Diagram

1-Wire Digital Thermometer

Related Application Notes

The following application notes can be applied to the DS18B20 and are available at

https://www.wendangku.net/doc/9115456588.html, .

Application Note 27: Understanding and Using Cyclic Redundancy Checks with Maxim iButton Products Application Note 122: Using Dallas’ 1-Wire ICs in 1-Cell

Li-Ion Battery Packs with Low-Side N-Channel Safety FETs Master

Application Note 126: 1-Wire Communication Through Software

Application Note 162: Interfacing the DS18x20/DS1822

1-Wire Temperature Sensor in a Microcontroller

Environment Application Note 208: Curve Fitting the Error of a Bandgap-Based Digital Temperature Sensor Application Note 2420: 1-Wire Communication with a Microchip PICmicro Microcontroller

Application Note 3754: Single-Wire Serial Bus Carries Isolated Power and Data

Sample 1-Wire subroutines that can be used in conjunc-tion with A pplication Note 74: Reading and Writing iBut-tons via Serial Interfaces can be downloaded from the Maxim website.

Figure 17. Detailed Master Read 1 Timing

Figure 18. Recommended Master Read 1 Timing

1-Wire Digital Thermometer

DS18B20 Operation Example 1

In this example there are multiple DS18B20s on the bus and they are using parasite power. The bus master initi-ates a temperature conversion in a specific DS18B20 and then reads its scratchpad and recalculates the CRC to verify the data. DS18B20 Operation Example 2

In this example there is only one DS18B20 on the bus and it is using parasite power. The master writes to the TH, TL, and configuration registers in the DS18B20 scratchpad and then reads the scratchpad and recalculates the CRC to verify the data. The master then copies the scratchpad contents to EEPROM.

MASTER MODE

DATA

(LSB FIRST)

COMMENTS

Tx Reset Master issues reset pulse.

Rx Presence DS18B20s respond with presence pulse.

Tx55h Master issues Match ROM command.

Tx 64-bit ROM

code

Master sends DS18B20 ROM

code.

Tx44h Master issues Convert T command.

Tx

DQ line

held high by

strong pullup

Master applies strong pullup

to DQ for the duration of the

conversion (t CONV).

Tx Reset Master issues reset pulse.

Rx Presence DS18B20s respond with presence pulse.

Tx55h Master issues Match ROM command.

Tx 64-bit ROM

code

Master sends DS18B20 ROM

code.

Tx BEh Master issues Read Scratchpad command.

Rx9 data bytes Master reads entire scratchpad

including CRC. The master then

recalculates the CRC of the

first eight data bytes from the

scratchpad and compares the

calculated CRC with the read

CRC (byte 9). If they match,

the master continues; if not, the

read operation is repeated.

MASTER

MODE

DATA (LSB

FIRST)

COMMENTS

Tx Reset Master issues reset pulse.

Rx Presence

DS18B20 responds with

presence pulse.

Tx CCh

Master issues Skip ROM

command.

Tx4Eh

Master issues Write Scratchpad

command.

Tx 3 data bytes

Master sends three data bytes

to scratchpad (T H, T L, and

config).

Tx Reset Master issues reset pulse.

Rx Presence

DS18B20 responds with

presence pulse.

Tx CCh

Master issues Skip ROM

command.

Tx BEh

Master issues Read Scratchpad

command.

Rx9 data bytes

Master reads entire scratchpad

including CRC. The master then

recalculates the CRC of the

first eight data bytes from the

scratchpad and compares the

calculated CRC with the read

CRC (byte 9). If they match,

the master continues; if not, the

read operation is repeated.

Tx Reset Master issues reset pulse.

Rx Presence

DS18B20 responds with

presence pulse.

Tx CCh

Master issues Skip ROM

command.

Tx48h

Master issues Copy Scratchpad

command.

Tx

DQ line

held high by

strong pullup

Master applies strong pullup to

DQ for at least 10ms while copy

operation is in progress.

1-Wire Digital Thermometer

+Denotes a lead-free package. A “+” will appear on the top mark of lead-free packages.

T&R = Tape and reel.

*TO-92 packages in tape and reel can be ordered with straight or formed leads. Choose “SL” for straight leads. Bulk TO-92 orders are straight leads only.

PART

TEMP RANGE PIN-PACKAGE TOP MARK DS18B20-55°C to +125°C 3 TO-9218B20DS18B20+-55°C to +125°C 3 TO-92

18B20DS18B20/T&R -55°C to +125°C 3 TO-92 (2000 Piece)18B20DS18B20+T&R -55°C to +125°C 3 TO-92 (2000 Piece)18B20 DS18B20-SL/T&R -55°C to +125°C 3 TO-92 (2000 Piece)*18B20DS18B20-SL+T&R -55°C to +125°C 3 TO-92 (2000 Piece)*18B20 DS18B20U -55°C to +125°C 8 FSOP 18B20DS18B20U+-55°C to +125°C 8 FSOP

18B20DS18B20U/T&R -55°C to +125°C 8 FSOP (3000 Piece)18B20DS18B20U+T&R -55°C to +125°C 8 FSOP (3000 Piece)18B20DS18B20Z -55°C to +125°C 8 SO DS18B20DS18B20Z+-55°C to +125°C 8 SO

DS18B20DS18B20Z/T&R -55°C to +125°C 8 SO (2500 Piece)DS18B20DS18B20Z+T&R -55°C to +125°C

8 SO (2500 Piece)

DS18B20

1-Wire Digital Thermometer

Ordering Information

REVISION DATE DESCRIPTION

PAGES CHANGED

030107

In the Absolute Maximum Ratings section, removed the reflow oven temperature value of +220°C. Reference to JEDEC specification for reflow remains.

19101207

In the Operation—Alarm Signaling section, added “or equal to” in the description for a TH alarm condition

5In the Memory section, removed incorrect text describing memory.

7In the Configuration Register section, removed incorrect text describing configuration register.

8042208In the Ordering Information table, added TO-92 straight-lead packages and included a note that the TO-92 package in tape and reel can be ordered with either formed or straight leads.21/15

Updated Benefits and Features section

1

1-Wire Digital Thermometer

Revision History

(完整版)DS18B20的工作原理

DS18B20的工作原理： DS18B20单线数字温度传感器是DALLAS半导体公司开发的适配微处理器的智能温度传感器。它具有3脚TO-92小体积封装形式。温度测量范围为-55℃--+125℃，可进行9-12位的编程，分辨率可达0.0625。被测温度用符号扩展的16位数字量方式串行输出。工作电压支持3V-5.5V，CPU只需一根端口线就能与诸多DS18B20通信，占用微处理器的端口较少。DS18B20采用3脚TO-92封装，引脚排列如图： DQ：数字信号端；GND：电源地；VDD：电源输入端 DS18B20的内部框图如图： 主要由寄生电源、64位激光ROM与单线接口、温度传感器、高速暂存器、触发寄存器、存储与控制逻辑、8位循环冗余校验码发生器组成。 测温电路原理： 低温度系数振荡器用于产生稳定的频率f，振荡频率受温度的影响很小，高温度系数振荡器将被测温度转化成频率信号，随温度变化其振荡频率明显改变。图中还隐含着计数门，当计数门打开时，DS18B20就对低温度振荡器产生的时钟脉冲进行计数，进而完成温度测量。计数门的开启时间由高温度系数振荡器来决定。每次测量前，首先将-55℃所对应的基数分别

置入减法计数器、温度寄存器中。在计数门关闭之前若计数器已减至零，温度寄存器中的数值就增加0.5℃。然后，计数器依斜率累加器的状态置入新的数值，再对时钟计数，然后减至零，温度寄存器值又增加0.5℃。只要计数门仍未关闭，就重复上诉过程，直至温度寄存器值达到被测温度值。 温度传感器的应用背景： 当今社会已经完全进入了电子信息化，温度控制器在各行各业中已经得到了充分的利用。具有对温度进行实时监控的功能，保证机器，测量仪器等等的正常运坐，他最大的特点是能实时监控周围温度的高低，并能同时控制电机运作来改变温度。现阶段运用于国内大部分家庭，系统效率越来越高，成本也越来越低。并可以根据其性质进行相应的改进运用于不同场合进行温度监测控制，比如仓库里、汽车里、电脑等等，带来大量的经济效益。可广泛应用于城市、农村、各种工业生产，在一定情况下也可以用于太阳能、锅炉及对温度敏感的产业的自动控制和温度报警，是实现无人值守的理想产品，市场极为广阔，需求量大。并且使用寿命长，适用范围广，安装及其容易。 智能风扇的应用： 传统的风扇大部分只有手动调速，再加一个定时器，功能单一。往往也存在一些隐患，如人们常常离开后忘记关闭风扇，浪费电且容易引发火灾，长时间工作还容易损坏电器。在如前半夜温度高，电风扇调的风速较高，但到了后半夜，温度下降，风速不会随气温变化，容易着凉，智能风扇的出现就能对环境进行检测，能随温度的变化而改变风速。 温度传感器的选择方案： 方案1：热敏电阻。 采用热敏电阻，可满足40摄氏度至90摄氏度的测量范围，但热敏电阻精度、重复性、可靠性比较差，对于检测1摄氏度的信号是不适用的。而且在温度测量系统中，是采用单片温度传感器，比如AD590,LM35等，但这些芯片输出的都是模拟信号，必须经过A/D转化后才能送给计算机，这样就使得测温装置的结构较复杂，另外，这种测温装置的一根线上只能挂一个传感器，不能进行多点测量，即使能实现，也要用到复杂的算法，一定程度上增加了软件实现的难度 方案2：DS18B20 DS18B20温度传感器是以9位数字量的形式反映器件的温度值，DS18B20通过一个单线接口发送或接受信息，因此在中央微处理器和DS18B20之间仅需一条连线（加上地线），用于读写和温度转化的电源可以从数据线本身获得，无需外部电源。它可以直接将模拟信号转化为数字信号，降低了电路的复杂程度，提高电路的运行质量。 综上，选择了方案2进行温度测量。 DS18B20的一般操作过程： 1：初始化 2：跳过ROM（命令CCH） 3：温度变换（命令44H）

DS18B20工作原理

DS18B20工作原理及时序 DS18B20原理与分析 DS18B20是美国DALLAS半导体公司继DS1820之后最新推出的一种改进型智能温度传感器。与传统的热敏电阻相比，他能够直接读出被测温度并且可根据实际要求通过简单的编程实现9～12位的数字值读数方式。可以分别在93.75 ms和750 ms内完成9位和12位的数字量，并且从DS18B20读出的信息或写入DS18B20的信息仅需要一根口线（单线接口）读写,温度变换功率来源于数据总线，总线本身也可以向所挂接的DS18B20供电，而无需额外电源。因而使用DS18B20可使系统结构更趋简单，可靠性更高。他在测温精度、转换时间、传输距离、分辨率等方面较DS1820有了很大的改进，给用户带来了更方便的使用和更令人满意的效果。 1.DS18B20简介 （1）独特的单线接口方式：DS18B20与微处理器连接时仅需要一条口线即可实现微处理器与DS18B20的双向通讯。 （2）在使用中不需要任何外围元件。 （3）可用数据线供电，电压范围：+3.0~ +5.5 V。 （4）测温范围：-55 ~+125 ℃。固有测温分辨率为0.5 ℃。 （5）通过编程可实现9~12位的数字读数方式。 （6）用户可自设定非易失性的报警上下限值。 （7）支持多点组网功能，多个DS18B20可以并联在惟一的三线上，实现多点测温。 （8）负压特性，电源极性接反时，温度计不会因发热而烧毁，但不能正常工作。 DS18B20的测温原理 DS18B20的测温原理如图2所示，图中低温度系数晶振的振荡频率受温度的影响很小〔1〕，用于产生固定频率的脉冲信号送给减法计数器1，高温度系数晶振随温度变化其震荡频率明显改变，所产生的信号作为减法计数器2的脉冲输入，图中还隐含着计数门，当计数门打开时，DS18B20就对低温度系数振荡器产生的时钟脉冲后进行计数，进而完成温度测量。计数门的开启时间由高温

单片机io口理解

【转】单片机IO口设置推挽和开漏的区别（转自网易博客冷水泡茶的日志）2010-09-28 13:43 单片机IO口设置推挽和开漏的区别 一般情况下我们在电路设计编程过程中设置单片机，大多是按照固有的模式去做的，做了几年这一行了，也没碰到过什么问题。昨天就遇到了这样一个问题，电路结构如图一，在这种情况下STC单片机与410单片机通讯是没问题的 但是与PC就无法通讯了，STC收不到PC的命令，以前410的位置是用的STC的片子一直没问题，我想也许是驱动能力不够，在410TX端加了上拉，不过没起作用。 用示波器监视串口得到面的波形 这说明sp3232下拉得不够，于是加了下拉，还是没起作用。又把410端口内部的上拉去掉，结果还是一样。 最后请教老师，在410程序里将TX的工作方式由推挽式改为开漏式，一切ok~！

从网上查了推挽和开漏的区别，放在这里免得以后再到处找了，给自己保存了 我们先来说说集电极开路输出的结构。集电极开路输出的结构如图1所示，右边的那个三极管集电极什么都不接，所以叫做集电极开路（左边的三极管为反相之用，使输入为“0”时，输出也为“0”）。对于图1，当左端的输入为“0”时，前面的三极管截止（即集电极C跟发射极E之间相当于断开），所以5V电源通过1K电阻加到右边的三极管上，右边的三极管导通（即相当于一个开关闭合）；当左端的输入为“1”时，前面的三极管导通，而后面的三极管截止（相当于开关断开）。 我们将图1简化成图2的样子。图2中的开关受软件控制，“1”时断开，“0”时闭合。很明显可以看出，当开关闭合时，输出直接接地，所以输出电平为0。而当开关断开时，则输出端悬空了，即高阻态。这时电平状态未知，如果后面一个电阻负载（即使很轻的负载）到地，那么输出端的电平就被这个负载拉到低电平了，所以这个电路是不能输出高电平的。 再看图三。图三中那个1K的电阻即是上拉电阻。如果开关闭合，则有电流从1K电阻及开关上流过，但由于开关闭其它三个口带内部上拉），当我们要使用输入功能时，只要将输出口设置为1即可，这样就相当于那个开关断开，而对于P0口来说，就是高阻态了。 对于漏极开路（OD）输出，跟集电极开路输出是十分类似的。将上面的三极管换成场效应管即可。这样集电极就变成了漏极，OC就变成了OD，原理分析是一样的。 另一种输出结构是推挽输出。推挽输出的结构就是把上面的上拉电阻也换成一个开关，当要输出高电平时，上面的开关通，下面的开关断；而要输出低电平时，则刚好相反。比起OC或者OD来说，这样的推挽结构高、低电平驱动能力都很强。如果两个输出不同电平的输出口接在一起的话，就会产生很大的电流，有可能将输出口烧坏。而上面说的OC或OD输出则不会有这样的情况，因为上拉电

DS18B20中文资料--最全版

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温度传感器工作原理

温度传感器工作原理 1.引脚★ ●GND接地。 ●DQ为数字信号输入\输出端。 ●VDD为外接电源输入端（在寄生电源接线方式时接地） 2.与单片机的连接方式★ 单线数字温度传感器DS18B20与单片机连接电路非常简单，引脚1接地（GND），引脚3（VCC）接电源+5V，引脚2（DQ）接单片机输入\输出一个端口，电压+5V和信号线（DQ）之间接有一个4.7k的电阻。 由于每片DS18B20含有唯一的串行数据口，所以在一条总线上可以挂接多个DS18B20芯片。 外部供电方式单点测温电路如图★ 外部供电方式多点测温电路如图★ 3.DS18B20的性能特点 DS18B20温度传感器是美国DALLAS半导体公司最新推出的一种改进型智能温度传感器。与传统的热敏电阻等测温元件相比，它能直接读出被测温度，并且可根据实际要求通过简单的编程实现9~12位的数字值读数方式。DS18B20的性能特点如下： ●独特的单线接口仅需要一个端口引脚进行通信。 ●多个DS18B20可以并联在唯一的三线上，实现多点组网功能。 ●不需要外部器件。 ●在寄生电源方式下可由数据线供电，电压围为3.0~5.5V。 ●零待机功耗。

●温度以9~12位数字量读出 ●用户可定义的非易失性温度报警设置。 ●报警搜索命令识别并标识超过程序限定温度（温度报警条件）的器件。 ●负电压特性，电源极性接反时，温度计不会因发热而烧毁，只是不能正常工作。 4.部结构 .DS18B20采用3脚PR—35封装或8脚SOIC封装，其部结构框图★ 64位ＲＯＭ的位结构如图★◆。开始８位是产品类型的编号；接着是每个器件的唯一序号，共有４８位；最后８位是前面５６位的ＣＲＣ检验码，这也是多个DS18B20可以采用单线进行通信的原因。非易失性温度报警触发器ＴＨ和ＴＬ，可通过软件写入用户报警上下限数据。 MSB LSB MSB LSB MSB LSB DS18B20温度传感器的部存储器还包括一个高速暂存RAM和一个非易失性的可电擦除的E2PROM。 高速暂存RAM的结构为9字节的存储器，结构如图★。前2字节包含测得的温度信息。第3和4字节是TH和TL的拷贝，是易失的，每次上电复位时被刷新。第5字节为配置寄存器，其容用于确定温度值的数字转换分辨率，DS18B20工作时按此寄存器中的分辨率将温度转化为相应精度的数值。该字节各位的定义如图★，其中，低5位一直为1；TM是测试模式位，用于设置DS18B20在工作模式还是在测试模式，在DS18B20出厂时，该位被设置为0，用户不要去改动；R0和R1决定温度转化的精度位数，即用来设置分辨率，其定义方法见表★ 高速暂存RAM的第6、7、8字节保留未用，表现为全逻辑1。第9字节是前面所有8

IO口工作原理

8051单片机I/O引脚工作原理 (2012-11-09 20:56:54) 转载▼ 标签： 杂谈 8051单片机I/O引脚工作原理 [转载] 一、P0端口的结构及工作原理 P0端口8位中的一位结构图见下图： 由上图可见，P0端口由锁存器、输入缓冲器、切换开关、一个与非门、一个与门及场效应管驱动电路构成。再看图的右边，标号为P0.X引脚的图标，也就是说P0.X引脚可以是P0.0到P0.7的任何一位，即在P0口有8个与上图相同的电路组成。 下面，我们先就组成P0口的每个单元部份跟大家介绍一下： 先看输入缓冲器：在P0口中，有两个三态的缓冲器，在学数字电路时，我们已知道，三态门有三个状态，即在其的输出端可以是高电平、低电平，同时还有一种就是高阻状态（或称为禁止状态），大家看上图，上面一个是读锁存器的缓冲器，也就是说，要读取D锁存器输出端Q的数据，那就得使读锁存器的这个缓冲器的三态控制端（上图中标号为‘读锁存器’端）有效。下面一个是读引脚的缓冲器，要读取P0.X引脚上的数据，也要使标号为‘读引脚’的这个三态缓

冲器的控制端有效，引脚上的数据才会传输到我们单片机的内部数据总线上。 D锁存器：构成一个锁存器，通常要用一个时序电路，时序的单元电路在学数字电路时我们已知道，一个触发器可以保存一位的二进制数（即具有保持功能），在51单片机的32根I/O口线中都是用一个D触发器来构成锁存器的。大家看上图中的D锁存器，D端是数据输入端，CP是控制端（也就是时序控制信号输入端），Q是输出端，Q非是反向输出端。 对于D触发器来讲，当D输入端有一个输入信号，如果这时控制端CP没有信号（也就是时序脉冲没有到来），这时输入端D的数据是无法传输到输出端Q及反向输出端Q非的。如果时序控制端CP的时序脉冲一旦到了，这时D端输入的数据就会传输到Q及Q非端。数据传送过来后，当CP时序控制端的时序信号消失了，这时，输出端还会保持着上次输入端D的数据（即把上次的数据锁存起来了）。如果下一个时序控制脉冲信号来了，这时D端的数据才再次传送到Q端，从而改变Q端的状态。 多路开关：在51单片机中，当内部的存储器够用（也就是不需要外扩展存储器时，这里讲的存储器包括数据存储器及程序存储器）时，P0口可以作为通用的输入输出端口（即I/O）使用，对于8031（内部没有ROM）的单片机或者编写的程序超过了单片机内部的存储器容量，需要外扩存储器时，P0口就作为‘地址/数据’总线使用。那么这个多路选择开关就是用于选择是做为普通I/O口使用还是作为‘数据/地址’总线使用的选择开关了。大家看上图，当多路开关与下面接通时，P0口是作为普通的I/O口使用的，当多路开关是与上面接通时，P0口是作为‘地址/数据’总线使用的。 输出驱动部份：从上图中我们已看出，P0口的输出是由两个MOS管组成的推拉式结构，也就是说，这两个MOS管一次只能导通一个，当V1导通时，V2就截止，当V2导通时，V1截止。 与门、与非门：这两个单元电路的逻辑原理我们在第四课数字及常用逻辑电路时已做过介绍，不明白的同学请回到第四节去看看。 前面我们已将P0口的各单元部件进行了一个详细的讲解，下面我们就来研究一下P0口做为I/O口及地址/数据总线使用时的具体工作过程。 1、作为I/O端口使用时的工作原理 P0口作为I/O端口使用时，多路开关的控制信号为0（低电平），看上图中的线线部份，多路开关的控制信号同时与与门的一个输入端是相接的，我们知道与门的逻辑特点是“全1出1，有0出0”那么控制信号是0的话，这时与门输出的也是一个0（低电平），与让的输出是0，V1管就截止，在多路控制开关的控制信号是0（低电平）时，多路开关是与锁存器的Q非端相接的（即P0口作为I/O口线使用）。 P0口用作I/O口线，其由数据总线向引脚输出（即输出状态Output）的工作过程：当写锁存器信号CP 有效，数据总线的信号→锁存器的输入端D→锁存器的反向输出Q非端→多路开关→V2管的栅极→V2的漏极到输出端P0.X。前面我们已讲了，当多路开关的控制信号为低电平0时，与门输出为低电平，V1管是截止的，所以作为输出口时，P0是漏极开路输出，类似于OC门，当驱动上接电

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温度传感器： DS18B20是DALLAS公司生产的一线式数字温度传感器，具有3引脚TO－92小体积封装形式；温度测量范围为－55℃～＋125℃,可编程为9位～12位A/D转换精度，测温分辨率可达0.0625℃，被测温度用符号扩展的16位数字量方式串行输出；其工作电源既可在远端引入，也可采用寄生电源方式产生；多个DS18B20可以并联到3根或2根线上，CPU只需一根端口线就能与诸多DS18B20通信，占用微处理器的端口较少，可节省大量的引线和逻辑电路。以上特点使DS18B20非常适用于远距离多点温度检测系统。 2 DS18B20的内部结构 DS18B20内部结构如图1所示，主要由4部分组成：64位ROM、温度传感器、非挥发的温度报警触发器TH和TL、配置寄存器。DS18B20的管脚排列如图2所示，DQ为数字信号输入／输出端；GND为电源地；VDD为外接供电电源输入端（在寄生电源接线方式时接地，见图4）。 ROM中的64位序列号是出厂前被光刻好的，它可以看作是该DS18B20的地址序列码，每个DS18B20的64位序列号均不相同。64位ROM的排的循环冗余校验码（CRC=X8＋X5＋X4＋1）。ROM的作用是使每一个DS18B20都各不相同，这样就可以实现一根总线上挂接多个DS18B20的目的。 图1 DS18B20的内部结构

图2DS18B20的管脚排列 DS18B20中的温度传感器完成对温度的测量，用16位符号扩展的二进制补码读数形式提供，以0.0625℃/LSB形式表达，其中S为符号位。例如＋125℃的数字输出为07D0H，＋25.0625℃的数字输出为0191H，－25.0625℃的数字输出为FF6FH，－55℃的数字输出为FC90H。 温度值高字节 高低温报警触发器TH和TL、配置寄存器均由一个字节的EEPROM组成，使用一个存储器功能命令可对TH、TL或配置寄存器写入。其中配置寄存器的格式如下： R1、R0决定温度转换的精度位数：R1R0=“00”，9位精度，最大转换时间为93.75ms；R1R0=“01”，10位精度，最大转换时间为187.5ms；R1R0=“10”，11位精度，最大转换时间为375ms；R1R0=“11”，12位精度，最大转换时间为750ms；未编程时默认为12位精度。 高速暂存器是一个9字节的存储器。开始两个字节包含被测温度的数字量信息；第3、4、5字节分别是TH、TL、配置寄存器的临时拷贝，每一次上电复位时被刷新；第6、7、8字节未用，表现为全逻辑1；第9字节读出的是前面所有8个字节的CRC码，可用来保证通信正确。 3 DS18B20的工作时序 DS18B20的一线工作协议流程是：初始化→ROM操作指令→存储器操作指令→数据传输。其工作时序包括初始化时序、写时序和读时序，如图3（a）（b）（c）所示。

单片机IO端口工作原理(P0端口,漏极开路,推挽,上拉电阻,准双向口)

单片机IO端口工作原理（P0端口,漏极开路,推挽,上拉电阻,准双向口） 一、P0端口的结构及工作原理 P0端口8位中的一位结构图见下图： 输入缓冲器：在P0口中，有两个三态的缓冲器，三态门有三个状态，即在其的输出端可以是高电平、低电平，同时还有一种就是高阻状态。图中有一个是读锁存器的缓冲器，也就是说，要读取D锁存器输出端Q的数据，那就得使读锁存器的这个缓冲器的三态控制端（上图中标号为‘读锁存器’端）有效。图中另一个是读引脚的缓冲器，要读取P0.X引脚上的数据，也要使标号为‘读引脚’的这个三态缓冲器的控制端有效，引脚上的数据才会传输到我们单片机的内部数据总线上。 D锁存器：一个触发器可以保存一位的二进制数（即具有保持功能），在51单片机的32根I/O口线中都是用一个D触发器来构成锁存器的。图中的锁存器，D 端是数据输入端，CP是控制端（也就是时序控制信号输入端），Q是输出端，Q 非是反向输出端。 对于D触发器来讲，当D输入端有一个输入信号，如果这时控制端CP没有信号（也就是时序脉冲没有到来），这时输入端D的数据是无法传输到输出端Q及反向输出端Q非的。如果时序控制端CP的时序脉冲一旦到了，这时D端输入的数据就会传输到Q及Q非端。数据传送过来后，当CP时序控制端的时序信号消失了，这时，输出端还会保持着上次输入端D的数据（即把上次的数据锁存起来了）。如果下一个时序控制脉冲信号来了，这时D端的数据才再次传送到Q端，从而改变Q端的状态。

多路开关：在51单片机中，当内部的存储器够用（也就是不需要外扩展存储器时，这里讲的存储器包括数据存储器及程序存储器）时，P0口可以作为通用的输入输出端口（即I/O）使用，对于8031（内部没有ROM）的单片机或者编写的程序超过了单片机内部的存储器容量，需要外扩存储器时，P0口就作为‘地址/数据’总线使用。那么这个多路选择开关就是用于选择是做为普通I/O口使用还是作为‘数据/地址’总线使用的选择开关了。大家看上图，当多路开关与下面接通时，P0口是作为普通的I/O口使用的，当多路开关是与上面接通时，P0口是作为‘地址/数据’总线使用的。 输出驱动部份：从上图中我们已看出，P0口的输出是由两个MOS管组成的推拉式结构，也就是说，这两个MOS管一次只能导通一个，当V1导通时，V2就截止，当V2导通时，V1截止。 还有与门、与非门。 1、作为I/O端口使用时的工作原理 P0口作为I/O端口使用时，多路开关的控制信号为0（低电平），图中与门输出的也是一个0（低电平），V1管就截止，且多路开关是与锁存器的Q非端相接的（即P0口作为I/O口线使用）。 P0口用作I/O口线，其由数据总线向引脚输出（即输出状态）的工作过程：当写锁存器信号CP有效，数据总线的信号→锁存器的输入端D→锁存器的反向输出Q非端→多路开关→V2管的栅极→V2的漏极到输出端P0.X。由于当多路开关的控制信号为低电平0时，与门输出为低电平，V1管是截止的，所以作为输出口时，P0是漏极开路输出，类似于OC门，当驱动上接电流负载时，需要外接上拉电阻。 下图就是由内部数据总线向P0口输出数据的流程图（红色箭头）。

温度传感器DS18B20工作原理

温度传感器:?DS１8B２０就是DAＬLAＳ公司生产得一线式数字温度传感器，具有３引脚ＴO－９2小体积封装形式；温度测量范围为—55℃～+1２5℃，可编程为9位～1２位A/D转换精度,测温分辨率可达0.0625℃，被测温度用符号扩展得16位数字量方式串行输出;其工作电源既可在远端引入,也可采用寄生电源方式产生；多个ＤＳ18B２0可以并联到3根或2根线上，CPＵ只需一根端口线就能与诸多DＳ18B20通信,占用微处理器得端口较少,可节省大量得引线与逻辑电路。以上特点使DS18B20非常适用于远距离多 点温度检测系统。 2DS１8B２0得内部结构??DS18B2０内部结构如图1所示,主要由4部分组成:64位ROＭ、温度传感器、非挥发得温度报警触发器TH与TL、配置寄存器。DＳ18B20得管脚排列如图2所示，DQ为数字信号输入／输出端；GNＤ为电源地;VＤD为外接供电电源输入端(在寄生电源接线方式时接地，见图4)。?ROM中得6４位序列号就是出厂前被光刻好得，它可以瞧作就是该DＳ18B２0得地址序列码，每个DＳ1８B２０得64位序列号均不相同.64位ＲＯＭ得排得循环冗余校验码(CRC=X8+Ｘ5+X4+1）。ROＭ得作用就是使每一个DS18B２０都各不相同，这样就可以实现一根总线上挂接多个ＤS1８Ｂ2０得目得。 ?图１DＳ18B20得内部结构 图2DS18B２0得管脚排列 DS18B20中得温度传感器完成对温度得测量,用16位符号扩展得二进制补码读数形式提供，以0。062５℃/ＬSＢ形式表达,其中S为符号位。例如+125℃得数字输出为07D0Ｈ，+2５。06２5℃得数字输出为0１９1H，-25.06２5℃得数字输出为FF６ＦH，－55℃得数字输出为FC90H。?温度值高字节? 高低温报警触发器TＨ与ＴL、配置寄存器均由一个字节得EEPRＯM组成，使用一个存储器功能命令可对TH、ＴL或配置寄存器写入。其中配置寄存器得格式如下：?Ｒ1、R0决定温度转换得精度位数:R1R0=“０

关于51单片机IO引脚驱动能力

单片机的引脚，可以用程序来控制，输出高、低电平，这些可算是单片机的输出电压。 但是，程序控制不了单片机的输出电流。单片机的输出电流，很大程度上是取决于引脚上的外接器件。 单片机输出低电平时，将允许外部器件，向单片机引脚内灌入电流，这个电流，称为“灌电流”，外部电路称为“灌电流负载”； 单片机输出高电平时，则允许外部器件，从单片机的引脚，拉出电流，这个电流，称为“拉电流”，外部电路称为“拉电流负载”。 这些电流一般是多少？最大限度是多少？这就是常见的单片机输出驱动能力的问题。 早期的51系列单片机的带负载能力，是很小的，仅仅用“能带动多少个TTL输入端”来说明的。 P1、P2和P3口，每个引脚可以都带动3个TTL输入端，只有P0口的能力强，它可以带动8个！ 分析一下TTL的输入特性，就可以发现，51单片机基本上就没有什么驱动能力。TTL输入基极的电流很小（一般为微安级的10uA-100uA）。 它的引脚，甚至不能带动当时的LED进行正常发光。（其工作电流一般为几个毫安到十几个毫安）。 记得是在AT89C51单片机流行起来之后，做而论道才发现：单片机引脚的能力大为增强，可以直接带动LED发光了。 看看下图，图中的D1、D2就可以不经其它驱动器件，直接由单片机的引脚控制发光显示。

虽然引脚已经可以直接驱动LED发光，但是且慢，先别太高兴，还是看看AT89C51单片机引脚的输出能力吧。 从AT89C51单片机的PDF手册文件中可以看到，稳态输出时，“灌电流”的上限为： Maximum IOL per port pin:10mA; Maximum IOL per8-bit port:Port0:26mA,Ports1,2,3:15mA; Maximum total I for all output pins:71mA. 这里是说： 每个单个的引脚，输出低电平的时候，允许外部电路，向引脚灌入的最大电流为10mA； 每个8位的接口（P1、P2以及P3），允许向引脚灌入的总电流最大为15mA，而P0的能力强一些，允许向引脚灌入的最大总电流为26mA； 全部的四个接口所允许的灌电流之和，最大为71mA。 而当这些引脚“输出高电平”的时候，单片机的“拉电流”能力呢？可以说是太差

DS18B20中文资料

第一部分：DS18B20的封装和管脚定义 首先，我们来认识一下DS18B20这款芯片的外观和针脚定义，DS18B20芯片的常见封装为TO-92，也就是普通直插三极管的样子，当然也可以找到以SO（DS18B20Z）和μSOP（DS18B20U）形式封装的产品，下面为DS18B20各种封装的图示及引脚图。 了解了这些该芯片的封装形式，下面就要说到各个管脚的定义了，如下表即

为该芯片的管脚定义： 上面的表中提到了一个“奇怪”的词——“寄生电源”，那我有必要说明一下了，DS18B20芯片可以工作在“寄生电源模式”下，该模式允许DS18B20工作在无外部电源状态，当总线为高电平时，寄生电源由单总线通过VDD 引脚，此时DS18B20可以从总线“窃取”能量，并将“偷来”的能量储存到寄生电源储能电容（Cpp）中，当总线为低电平时释放能量供给器件工作使用。所以，当DS18B20工作在寄生电源模式时，VDD引脚必须接地。 第二部分：DS18B20的多种电路连接方式 如下面的两张图片所示，分别为外部供电模式下单只和多只DS18B20测温系统的典型电路连接图。 （1）外部供电模式下的单只DS18B20芯片的连接图

（2）外部供电模式下的多只DS18B20芯片的连接图 这里需要说明的是，DS18B20芯片通过达拉斯公司的单总线协议依靠一个单线端口通讯，当全部器件经由一个三态端口或者漏极开路端口与总线连接时，控制线需要连接一个弱上拉电阻。在多只DS18B20连接时，每个DS18B20都拥有一个全球唯一的64位序列号，在这个总线系统中，微处理器依靠每个器件独有的64位片序列号辨认总线上的器件和记录总线上的器件地址，从而允许多只DS18B20同时连接在一条单线总线上，因此，可以很轻松地利用一个微处理器去控制很多分布在不同区域的DS18B20，这一特性在环境控制、探测建

DS18B20温度传感器工作原理及其应用电路图

DS18B20温度传感器工作原理及其应用电路图 时间：2012-02-16 14:16:04 来源：赛微电子网作者： 前言 温度与工农业生产密切相关，对温度的测量和控制是提高生产效率、保证产品质量以及保障生产安全和节约能源的保障。随着工业的不断发展，由于温度测量的普遍性，温度传感器的市场份额大大增加，居传感器首位。数字化温度传感器DS18B20是世界上第一片支持“一线总线”接口的温度传感器。现在，新一代的DS18B20温度传感器体积更小、更经济、更灵活。DS18B20温度传感器测量温度范围为-55℃～+125℃。在-10℃～+85℃范围内，精度为±0.5℃。现场温度直接以“一线总线”的数字方式传输，大大提高了系统的抗干扰性。基于DS18B20温度传感器的重要性，小编整理出DS18B20温度传感器工作原理及其应用电路图供大家参考。 一、DS18B20温度传感器工作原理（热电阻工作原理） DS18B20温度传感器工作原理框图如图所示： DS18B20温度传感器工作原理框图 图中低温度系数晶振的振荡频率受温度影响很小，用于产生固定频率的脉冲信号送给计数器1。高温度系数晶振随温度变化其振荡频率明显改变，所产生的信号作为计数器2的脉冲输入。计数器1和温度寄存器被预置在-55℃所对应的一个基数值。计数器1对低温度系数晶振产生的脉冲信号进行减法计数，当计数器1的预置值减到0时，温度寄存器的值将加1，计数器1的预置将重新被装入，计数器1重新开始对低温度系数晶振产生的脉冲信号进行计数，如此循环直到计数器2计数到0时，停止温度寄存器值的累加，此时温度寄存器中的数值即为所测温度。斜率累加器用于补偿和修正测温过程中的非线性，其输出用于修正计数器1的预置值。 二、DS18B20温度传感器的应用电路 1.DS18B20温度传感器寄生电源供电方式电路图 寄生电源方式特点： (1)进行远距离测温时，无须本地电源。 (2)可以在没有常规电源的条件下读取ROM。 (3)电路更加简洁，仅用一根I/O口实现测温。 (4)只适应于单一温度传感器测温情况下使用，不适于采用电池供电系统中。

单片机IO口结构与工作原理

一、P0端口的结构及工作原理 P0端口8位中的一位结构图见下图： 由上图可见，P0端口由锁存器、输入缓冲器、切换开关、一个与非门、一个与门及场效应管驱动电路构成。 下面，先分析组成P0口的各个部分： 先看输入缓冲器：在P0口中，有两个三态的缓冲器，在其的输出端可以是高电平、低电平，同时还有一种就是高阻状态（或称为禁止状态），上面一个是读锁存器的缓冲器，下面一个是读引脚的缓冲器，读取P0.X引脚上的数据，要使这个三态缓冲器有效，引脚上的数据才会传输到部数据总线上。 D锁存器：在51单片机的32根I/O口线中都是用一个D触发器来构成锁存器的。D端是数据输入端，CP是控制端（也就是时序控制信号输入端），Q是输出端，Q非是反向输出端。 多路开关：在51单片机中，不需要外扩展存储器时，P0口可以作为通用的输入输出端口（即I/O）使用，对于8031（部没有ROM）的单片机或者编写的程序超过了单片机部的存储器容量，需要外扩存储器时，P0口就作为‘地址/数据’总线使用。这个多路选择开关就是用于选择是做为普通I/O口使用还是作为‘数据/地址’总线使用的选择开关了。当多路开关与下面接通时，P0口是作为普通的I/O口使用的，当多路开关是与上面接通时，P0口是作为‘地址/数据’总线使用的。 输出驱动部份：P0口的输出是由两个MOS管组成的推拉式结构，也就是说，这两个MOS管一次只能导通一个，当V1导通时，V2就截止，当V2导通时，V1截止。

P0口作为I/O端口使用时，多路开关的控制信号为0（低电平），V1管截止，多路开关是与锁存器的Q非端相接的（即P0口作为I/O口线使用）。作为地址/数据线使用时，多路开关的控制信号为1，V1管由地址/数据线决定，多路开关与地址/数据线连接。 输出过程： 1、I/O输出工作过程：当写锁存器信号CP有效，数据总线的信号→锁存器的输入端D→锁存器的反向输出Q非端→多路开关→V2管的栅极→V2的漏极到输出端P0.X。这时多路开关的控制信号为低电平0，V1管是截止的，所以作为输出口时，P0是漏极开路输出，类似于OC门，当驱动上接电流负载时，需要外接上拉电阻。 下图就是由部数据总线向P0口输出数据的流程图（红色箭头）。 2、地址输出过程 控制信号为1，地址信号为“0”时，与门输出低电平，V1管截止；反相器输出高电平，V2管导通，输出引脚的地址信号为低电平。

18B20应用手册

DoYoung 电子技术—创造独立资源！ 18B20温度传感器应用解析 DoYoung 原创 V2.0 2007.3.16 DS18B20 温度传感器的种类众多，在应用与高精度、高可靠性的场合时DALLAS（达拉斯）公司生产的DS18B20温度传感 器当仁不让。超小的体积，超低的硬件开消，抗干扰能力强，精度高，附加功能强，使得DS18B20更受欢迎。对于我 们普通的电子爱好者来说，DS18B20的优势更是我们学习单片机技术和开发温度相关的小产品的不二选择。了解其工 作原理和应用可以拓宽您对单片机开发的思路。 DS18B20的主要特征： .. 全数字温度转换及输出。 .. 先进的单总线数据通信。 .. 最高12位分辨率，精度可达土0.5摄氏度。 .. 12位分辨率时的最大工作周期为750毫秒。 .. 可选择寄生工作方式。 .. 检测温度范围为–55°C ~+125°C (–67°F ~+257°F) .. 内置EEPROM，限温报警功能。 .. 64位光刻ROM，内置产品序列号，方便多机挂接。 .. 多样封装形式，适应不同硬件系统。

DS18B20芯片封装结构： 图1 DS18B20引脚功能：·GND 电压地·DQ 单数据总线·VDD 电源电压·NC 空引脚DS18B20工作原理及应用： DS18B20的温度检测与数字数据输出全集成于一个芯片之上，从而抗干扰力更强。其一个工作周期可分为两个部分，即温度检测和数据处理。在讲解其工作流程之前我们有必要了解18B20的内部存储器资源。18B20共有三种形态的存储器资源，它们分别是：ROM 只读存储器，用于存放DS18B20ID编码，其前8位是单线系列编码（DS18B20的编码是19H），后面48位是芯片唯一的序列号，最后8位是以上56的位的CRC码（冗余校验）。数据在出产时设置不由用户更改。DS18B20共64位ROM。 RAM 数据暂存器，用于内部计算和数据存取，数据在掉电后丢失，DS18B20共9个字节RAM，每个字节为8位。第1、2个字节是温度转换后的数据值信息，第3、4个字节是用户EEPROM（常用于温度报警值储存）的镜像。在上电复位时其值将被刷新。第5个字节则是用户第3个EEPROM的镜像。第6、7、8个字节为计数寄存器，是为了让用户得到更高的温度分辨率而设计的，同样也是内部温度转换、计算的暂存单元。第9个字节为前8个字节的CRC码。EEPROM 非易失性记忆体，用于存放长期需要保存的数据，上下限温度报警值和校验数据，DS18B20共3位EEPROM，并在RAM都存在镜像，以方便用户操作。

单片机IO口结构及工作原理

、Po端口的结构及工作原理 Po端口8位中的一位结构图见下图: 地址∕ttiκ I i O i XWwfr?? 内部总线 i?引脚 PO 口工作康理图 由上图可见，P0端口由锁存器、输入缓冲器、切换开关、一个与非门、一个与门及场效应管驱动电路构成下面，先分析组成P0 口的各个部分： 先看输入缓冲器：在P0 口中，有两个三态的缓冲器，在其的输出端可以是高电平、低电平，同时还有一种就是高阻状态（或称为禁止状态），上面一个是读锁存器的缓冲器，下面一个是读引脚的缓冲器，读取P0.X引脚上的数据，要使这 个三态缓冲器有效，引脚上的数据才会传输到内部数据总线上。 D锁存器：在51单片机的32根I/O 口线中都是用一个D触发器来构成锁存器的。D 端是数据输入端，CP是控制端（也就是时序控制信号输入端），Q是输出端，Q非是反向输出端。 多路开关：在51单片机中，不需要外扩展存储器时，P0 口可以作为通用的输入输出端口（即I/O）使用，对于8031 （内部没有ROM ）的单片机或者编写的程序超过了单片机内部的存储器容量，需要外扩存储器时，P0 口就作为,地址/数据? 总线使用。这个多路选择开关就是用于选择是做为普通I/O 口使用还是作为，数据/地址?总线使用的选择开关了。当多路开关与下面接通时，P0 口是作为普通的I/O 口使用的，当多路开关是与上面接通时，P0 口是作为,地址/数据？总线使用的。 输出驱动部份：P0 口的输出是由两个MOS管组成的推拉式结构，也就是说，这两个MOS管一次只能导通一个，当V1导通时，V2就截止，当V2导通时，V1截止。

Po 口作为I/O端口使用时，多路开关的控制信号为0 （低电平）,V1管截止, 多路开关是与锁存器的Q非端相接的（即P0 口作为I/O 口线使用）。作为地址/数据线使用时，多路开关的控制信号为1，V1管由地址/数据线决定，多路开关与地址/数据线连接。 输出过程： 1、I/O输出工作过程：当写锁存器信号CP有效，数据总线的信号→锁存器的输入端D→锁存器的反向输出Q非端→多路开关→V2管的栅极→V2的漏极到输出端 P0.X。这时多路开关的控制信号为低电平0, V1管是截止的，所以作为输出口时，P0是漏极开路输出，类似于OC门，当驱动上接电流负载时，需要外接上拉电阻。下图就是由内部数据总线向P0 口输出数据的流程图（红色箭头）。 地址/数抵 控制信号（0. 1） PO. XWftKra 内部总线 ht t p://WWW Z Po口由内部致据忌址向31 Wtt出时的5t?≡ 2、地址输出过程 控制信号为1 ,地址信号为“（时，与门输出低电平，V1管截止；反相器输出高电平，V2管导通，输出引脚的地址信号为低电平。

DS18B20数据手册-中文版

概述 DS18B20数字温度传感器提供9-Bit 到12-Bit的摄氏温度测量精度和一个用户可编程的非易失性且具有过温和低温触发报警的报警功能。DS18B20采用的1-Wire通信即仅采用一个数据线（以及地）与微控制器进行通信。该传感器的温度检测范围为-55℃至+125℃，并且在温度范围超过-10℃至85℃之外时还具有+-0.5℃的精度。此外，DS18B20可以直接由数据线供电而不需要外部电源供电。 每片DS18B20都有一个独一无二的64位序列号，所以一个1-Wire总线上可连接多个DS18B20设备。因此，在一个分布式的大环境里用一个微控制器控制多个DS18B20是非常简单的。这些特征使得其在HV AC环境控制，在建筑、设备及机械的温度监控系统，以及温度过程控制系统中有着很大的优势。 特性 ·独特的1-Wire总线接口仅需要一个管脚来通信。 ·每个设备的内部ROM上都烧写了一个独一无二的64位序列号。 ·多路采集能力使得分布式温度采集应用更加简单。 ·无需外围元件。 ·能够采用数据线供电；供电范围为3.0V至5.5V。 ·温度可测量范围为：-55℃至+125℃（-67℉至+257℉）。 ·温度范围超过-10℃至85℃之外时具有+-0.5℃的精度。 ·内部温度采集精度可以由用户自定义为9-Bits至12-Bits。 DS18B20 分辨率可编程 1-Wire数字温度传感器 ·温度转换时间在转换精度为12-Bits时达到最大值750ms。 ·用户自定义非易失性的的温度报警设置。·定义了温度报警搜索命令和当温度超过用户自定义的设定值时。 ·可选择的8-Pin SO (150 mils), 8-PinμSOP，及3-Pin TO-92封装。 ·与DS1822程序兼容。 ·应用于温度控制系统，工业系统，民用产品，温度传感器，或者任何温度检测系统中。 管脚定义图

IO结构和工作原理

单片机IO口结构及上拉电阻 MCS-51有4组8位I/O口：P0、P1、P2和P3口，P1、P2和P3为准双向口，P0口则为双向三态输入输出口，下面我们分别介绍这几个口线。 一、P0口和P2口 图1和图2为P0口和P2口其中一位的电路图。由图可见，电路中包含一个数据输出锁存器（D触发器）和两个三态数据输入缓冲器，另外还有一个数据输出的驱动（T1和T2）和控制电路。这两组口线用来作为CPU与外部数据存储器、外部程序存储器和I/O扩展口，而不能象P1、P3直接用作输出口。它们一起可以作为外部地址总线，P0口身兼两职，既可作为地址总线，也可作为数据总线。 图1 单片机P0口内部一位结构图 图2 单片机P0口内部一位结构图 P1口作为外部数据存储器或程序存储器的地址总线的高8位输出口 AB8-AB15，P0口由ALE选通作为地址总线的低8位输出口AB0-AB7。外部的程序

存储器由PSEN信号选通，数据存储器则由WR和RD读写信号选通，因为2^16=64k，所以MCS-51最大可外接64kB的程序存储器和数据存储器。 二、P1口 图3为P2口其中一位的电路图，P1口为8位准双向口，每一位均可单独定义为输入或输出口，当作为输出口时，1写入锁存器，Q(非)=0，T2截止，内上拉电阻将电位拉至"1"，此时该口输出为1，当0写入锁存器，Q(非)=1,T2导通，输出则为0。 图3 单片机P2口内部一位结构图 作为输入口时，锁存器置1，Q(非)=0，T2截止，此时该位既可以把外部电路拉成低电平，也可由内部上拉电阻拉成高电平，正因为这个原因，所以P1口常称为准双向口。 需要说明的是，作为输入口使用时，有两种情况: 1.首先是读锁存器的内容，进行处理后再写到锁存器中，这种操作即读—修改—写操作，象JBC(逻辑判断)、CPL(取反)、INC(递增)、DEC(递减)、ANL(与逻辑)和ORL(逻辑或)指令均属于这类操作。 2.读P1口线状态时，打开三态门G2,将外部状态读入CPU。 三、P3口 P3口的电路如图4所示，P3口为准双向口，为适应引脚的第二功能的需要，增加了第二功能控制逻辑，在真正的应用电路中，第二功能显得更为重要。由于第二功能信号有输入输出两种情况，我们分别加以说明。