DS18S20 查看數據表（PDF） - Dallas Semiconductor -> Maxim Integrated

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DS18S20

High Precision 1-Wire® Digital Thermometer

Dallas Semiconductor -> Maxim Integrated 

DS18S20

INITIALIZATION

All transactions on the 1–Wire bus begin with an initialization 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 presence pulse lets the bus master know that the DS18S20 is on the bus and is ready to operate. For

more details, see the “1–Wire Signaling” section.

ROM FUNCTION COMMANDS

Once the bus master has detected a presence, it can issue one of the five ROM function commands. All

ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart in

Figure 5):

Read ROM [33h]

This command allows the bus master to read the DS18S20’s 8–bit family code, unique 48–bit serial

number, and 8–bit CRC. This command can only be used if there is a single DS18S20 on the bus. If

more than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the

same time (open drain will produce a wired AND result).

Match ROM [55h]

The match ROM command, followed by a 64–bit ROM sequence, allows the bus master to address a

specific DS18S20 on a multidrop bus. Only the DS18S20 that exactly matches the 64–bit ROM sequence

will respond to the following memory function command. All slaves that do not match the 64–bit ROM

sequence will wait for a reset pulse. This command can be used with a single or multiple devices on the

bus.

Skip ROM [CCh]

This command can save time in a single drop bus system by allowing the bus master to access the

memory functions without providing the 64–bit ROM code. If more than one slave is present on the bus

and a Read command is issued following the Skip ROM command, data collision will occur on the bus as

multiple slaves transmit simultaneously (open drain pulldowns will produce a wired AND result).

Search ROM [F0h]

When a system is initially brought up, the bus master might not know the number of devices on the

1-Wire bus or their 64–bit ROM codes. The search ROM command allows the bus master to use a

process of elimination to identify the 64–bit ROM codes of all slave devices on the bus.

Alarm Search [ECh]

The flowchart of this command is identical to the Search ROM command. However, the DS18S20 will

respond to this command only if an alarm condition has been encountered at the last temperature

measurement. An alarm condition is defined as a temperature higher than TH or lower than TL. The

alarm condition remains set as long as the DS18S20 is powered up, or until another temperature

measurement reveals a non–alarming value. For alarming, the trigger values stored in EEPROM are

taken into account. If an alarm condition exists and the TH or TL settings are changed, another

temperature conversion should be done to validate any alarm conditions.

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