DS28EA00U+T&R【PDF 25/29 页】IC THERMOMETER 1-WIRE 8-USOP

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through R

of the PIOA pin charges the PIOA/PIOB

connections to logic 1 level at all devices except for the

first device in the chain. If a local V

supply is not

available, the master needs to activate a low-imped-

ance bypass to the 1-Wire pullup resistor immediately

after the inverted chain control byte until the PIOA/PIOB

connections have reached a voltage equivalent to the

logic 1 level.

First Cycle: The master sends a Conditional Read ROM

command, which causes the first device in the chain to

respond with its 64-bit registration number. The master

memorizes the registration number and the fact that this

is the first device in the chain. Next, the master transmits

a Chain DONE command. Through the PIOA pin of the

just discovered device, this asserts logic 0 at the PIOB

pin of the second device in the chain and also prevents

the just discovered device from responding again.

Second Cycle: The master sends a Conditional Read

ROM command. Since the second DS28EA00 is the

only device in the chain with a low level at PIOB, it

responds with its registration number. The master

stores the registration number with the sequence num-

ber of 2. The first device cannot respond since it is in

chain DONE state. Next, the master transmits a Chain

DONE command.

Additional Cycles: To identify the registration numbers

of the remaining devices and their physical sequence,

the master repeats the steps of Conditional Read ROM

and Chain DONE. If there is no response to Conditional

Read ROM, all devices in the chain are identified.

Ending Condition: At the end of the discovery process

all devices in the chain are in the chain DONE state.

The master should end the sequence discovery by

issuing a Skip ROM command followed by a Chain OFF

command. This puts all the devices into the chain OFF

state and transfers control of the PIOB and PIOA pins to

the PIO Access Read and Write function commands.

1-Wire Digital Thermometer with

Sequence Detect and PIO

DS28EA00

Maxim Integrated

PUP

REH

CASE A

CASE C

CASE B

Figure 14. Noise Suppression Scheme

DS28EA00

PIOB

PIOA

GND

*CAPACITANCE OF THE CABLING BETWEEN ADJACENT DEVICES IN THE CHAIN.

1-Wire

MASTER

DS28EA00

PIOB

PX. Y

MICROCONTROLLER

PIOA

GND

DS28EA00

PIOB

PIOA

GND

Figure 15. DS28EA00 Wired for Sequence Discovery (Chain Function)

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