DS28EA00U+T&R【PDF 5/29 页】IC THERMOMETER 1-WIRE 8-USOP

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1-Wire Digital Thermometer with

Sequence Detect and PIO

DS28EA00

Maxim Integrated

Pin Description

NAME

FUNCTION

1-Wire Bus Interface and Parasitic Power Supply. Open-drain pin that requires external pullup

resistor.

2, 3, 5

N.C.

No Connection

GND

Ground Supply

PIOA (DONE)

Open-Drain PIOA Channel and Chain Output. For sequence detection, PIOA must be connected to

PIOB of the next device in the chain; leave open or connect to GND for the last device in the

chain.

PIOB (EN)

Open-Drain PIOB Channel and Chain Input. For sequence detection, PIOB of the first device in the

chain must be connected to GND.

Power Supply. Must be connected to GND for operation in parasite-power mode.

Detailed Description

The Block Diagram shows the relationships between

the major function blocks of the DS28EA00. The device

has three main data components: 64-bit registration

number, 64-bit scratchpad, and alarm and configura-

tion registers. The 1-Wire ROM function control unit

processes the ROM function commands that allow the

device to function in a networked environment. The

device function control unit implements the device-spe-

cific control functions, such as read/write, temperature

conversion, setting the chain state for sequence detec-

tion, and PIO access. The cyclic redundancy check

(CRC) generator assists the master verifying data

integrity when reading temperatures and memory data.

In the sequence-detect process, PIOB functions as an

input, while PIOA provides the connection to the next

device. The power-supply sensor allows the master to

remotely read whether the DS28EA00 has local power

available.

Figure 1 shows the hierarchical structure of the 1-Wire

protocol. The bus master must first provide one of the

eight ROM function commands: Read ROM, Match

ROM, Search ROM, Conditional (Alarm) Search ROM,

Conditional Read ROM, Skip ROM, Overdrive-Skip

ROM, Overdrive-Match ROM.

Upon completion of an overdrive ROM command exe-

cuted at standard speed, the device enters overdrive

mode, where all subsequent communication occurs at

a higher speed. The protocol required for these ROM

function commands is described in Figure 11. After a

ROM function command is successfully executed, the

device-specific control functions become accessible

and the master can provide any one of the nine avail-

able commands. The protocol for these control function

commands is described in Figure 9. All data is read

and written least significant (LS) bit first.

64-Bit Registration Number

Each DS28EA00 contains a unique registration number

that is 64 bits long. The first 8 bits are a 1-Wire family

code. The next 48 bits are a unique serial number. The

last 8 bits are a CRC of the first 56 bits (see Figure 2 for

details). The 1-Wire CRC is generated using a polyno-

mial generator consisting of a shift register and XOR

gates as shown in Figure 3. The polynomial is X

+ X

+ 1. Additional information about the 1-Wire CRC is

available in Application Note 27: Understanding and

Using Cyclic Redundancy Checks with Maxim i

Button

?/DIV>

Products.

The shift register bits are initialized to 0. Then starting

with the least significant bit of the family code, one bit

at a time is shifted in. After the eighth bit of the family

code has been entered, then the 48-bit serial number is

entered. After the last byte of the serial number has

been entered, the shift register contains the CRC value.

Shifting in the 8 bits of CRC returns the shift register to

all 0s.

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

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