Rainbow-electronics DS18B20 Manual de usuario descargar pdf (Pagina 15)

DS18B20

15 of 20

The DS18B20 samples the 1-wire bus during a window that lasts from 15 µs to 60 µs after the master

initiates the write time slot. If the bus is high during the sampling window, a 1 is written to the

DS18B20. If the line is low, a 0 is written to the DS18B20.

READ/WRITE TIME SLOT TIMING DIAGRAM Figure 14

READ TIME SLOTS

The DS18B20 can only transmit data to the master when the master issues read time slots. Therefore, the

master must generate read time slots immediately after issuing a Read Scratchpad [BEh] or Read Power

Supply [B4h] command, so that the DS18B20 can provide the requested data. In addition, the master can

generate read time slots after issuing Convert T [44h] or Recall E

[B8h] commands to find out the status

of the operation as explained in the DS18B20 FUNCTION COMMAND section.

All read time slots must be a minimum of 60 µs in duration with a minimum of a 1 µs recovery time

between slots. A read time slot is initiated by the master device pulling the 1-wire bus low for a

minimum of 1 µs and then releasing the bus (see Figure 14). After the master initiates the read time slot,

the DS18B20 will begin transmitting a 1 or 0 on bus. The DS18B20 transmits a 1 by leaving the bus high

and transmits a 0 by pulling the bus low. When transmitting a 0, the DS18B20 will release the bus by the

end of the time slot, and the bus will be pulled back to its high idle state by the pullup resister. Output

data from the DS18B20 is valid for 15 µs after the falling edge that initiated the read time slot.

µµ

µs

µµ

µs

GND

1-WIRE BUS

µµ

µs < T

“0” < 120

1 µ

µµ

µs < T

REC

< ∞

DS18B20 Samples

MIN TYP MA

µµ

µs

µµ

µs

> 1

µµ

µs

MASTER WRITE “0” SLOT MASTER WRITE “1” SLOT

GND

1-WIRE BUS

µµ

µs

MASTER READ “0” SLOT MASTER READ “1” SLOT

Master samples

START

OF SLOT

START

OF SLOT

> 1

µµ

µs

1 µ

µµ

µs < T

REC

< ∞

µµ

µs 15

µµ

µs

µµ

µs

µµ

µs

DS18B20 Samples

MIN TYP MA

LINE TYPE LEGEND

Bus master pulling low DS18B20 pulling low

Resistor pullup

> 1

µµ

µs

1 2 ... 10 11 12 13 14 15 16 17 18 19 20

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Rainbow-electronics DS18B20 Manual de usuario Pagina 15

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