DS28EA00U+T&R【PDF 9/29 页】IC THERMOMETER 1-WIRE 8-USOP

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The functional assignments of the individual bits are

explained in the table below. Bits [4:0] and bit 7 have

no function and cannot be changed by the user. As a

factory default, the device operates in 12-bit resolution.

1-Wire Digital Thermometer with

Sequence Detect and PIO

DS28EA00

Maxim Integrated

ADDRRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

BIT DESCRIPTION

BIT(S)

DEFINITION

R1, R0: Temperature

Converter Resolution

[6:5]

These bits control the resolution of the temperature converter. The codes are as follows:

9 bits

10 bits

11 bits

12 bits

DEVICE BEHAVIOR

CHAIN STATE

PIOB (EN)

PIOA (DONE)

CONDITIONAL READ ROM

OFF (Default)

PIO (High Impedance)

Not Recognized

EN Input

Pullup On

Recognized if EN is 0

DONE

No Function

Pulldown On (DONE Logic 0)

Not Recognized

Table 2. Chain States

PIO Structure

Each PIO consists of an open-drain pulldown transistor

and an input path to read the pin state. The transistor is

controlled by the PIO output latch, as shown in Figure

5. The device function control unit connects the PIO

pins logically to the 1-Wire interface. PIOA has a pullup

path to internal V

to facilitate the sequence-detect

function (see the Block Diagram) in conjunction with the

Chain command; PIOB is truly an open-drain structure.

The power-on default state of the PIO output transistors

is off; high-impedance, on-chip resistors (not shown in

Figure 5) pull the PIO pins to internal V

Chain Function

The chain function is a feature that allows the 1-Wire

master to discover the physical sequence of devices

that are wired as a linear network (chain). This is partic-

ularly convenient for devices that are installed at equal

spacing along a long cable (e.g., to measure tempera-

tures at different locations inside a storage tower or

tank). Without chain function, the master needs a

lookup table to correlate the registration number to the

physical location.

The chain function requires two pins: an input (EN) to

enable a device to respond during the discovery and

an output (DONE) to inform the next device in the chain

that the discovery of its neighbor is done. The two gen-

eral-purpose ports of the DS28EA00 are reused for the

chain function. PIOB functions as an EN input and PIOA

generates the DONE signal, which is connected to the

EN input of the next device, as shown in the Typical

Operating Circuit. The EN input of the first device in the

chain needs to be hardwired to GND or logic 0 must be

applied for the duration of the sequence discovery

process. Besides the two pins, the sequence discovery

relies on the Conditional Read ROM command.

For the chain function and normal PIO operation to

coexist, the DS28EA00 distinguishes three chain states:

OFF, ON, and DONE. The transition from one chain

state to another is controlled through the Chain com-

mand. Table 2 summarizes the chain states and the

specific behavior of the PIO pins.

PIO OUTPUT LATCH

CLOCK

PIO PIN

PIO PIN STATE

PIO OUTPUT LATCH STATE

PIO DATA

PIO CLOCK

Figure 5. PIO Simplified Logic Diagram

Configuration Register

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