DS1822+ Maxim Integrated Products, DS1822+ Datasheet - Page 10

• Manufacturer Part Number: DS1822+
• Description: Board Mount Temperature Sensors IC THERMOMETER ECONO DIG
• Manufacturer: Maxim Integrated Products

Specifications of DS1822+

• Temperature Threshold: Programmable
• Full Temp Accuracy: +/- 2 C
• Package / Case: TO-92
• Digital Output - Bus Interface: 1-Wire
• Digital Output - Number Of Bits: 9 bit to 12 bit
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 3 V
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 55 C
• Output Type: Digital
• Supply Current: 1.5 mA
• Ic Output Type: Digital
• Sensing Accuracy Range: ± 2°C
• Supply Voltage Range: 3V To 5.5V
• Resolution (bits): 12bit
• Sensor Case Style: TO-92
• No. Of Pins: 3
• Accuracy %: 2°C
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

DS1822
TRANSACTION SEQUENCE
The transaction sequence for accessing the DS1822 is as follows:
Step 1. Initialization
Step 2. ROM Command (followed by any required data exchange)
Step 3. DS1822 Function Command (followed by any required data exchange)
It is very important to follow this sequence every time the DS1822 is accessed, as the DS1822 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. 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 slave devices (such as the DS1822) 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 DS1822 function command. A flowchart for
operation of the ROM commands is shown in Figure 11.
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. If there is only one slave on the bus, the simpler Read ROM command (see below)
can be used in place of the Search ROM process. For a detailed explanation of the Search ROM
procedure, refer to the iButton Book of Standards at www.ibutton.com/ibuttons/standard.pdf. 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 procedure. 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.
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