Read/write time slot timing diagram figure 14, Read time slots – Rainbow Electronics DS18B20 User Manual

Page 15

DS18B20

15 of 20

The DS18B20 samples the 1-wire bus during a window that lasts from 15

s to 60

s 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

s in duration with a minimum of a 1

s 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

s 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

s after the falling edge that initiated the read time slot.

µµµµ

GND

1-WIRE BUS

µµµµ

s < T

“0” < 120

µµµµ

s < T

REC

∞

DS18B20

Samples

MIN TYP MAX

µµµµ

> 1

µµµµ

MASTER WRITE “0” SLOT

MASTER WRITE “1” SLOT

GND

1-WIRE BUS

µµµµ

MASTER READ “0” SLOT

MASTER READ “1” SLOT

Master samples

START

OF SLOT

START

OF SLOT

> 1

µµµµ

s < T

REC

∞

µµµµ

DS18B20

Samples

MIN TYP MAX

LINE TYPE LEGEND

Bus master pulling low

DS18B20 pulling low

Resistor

pullup

> 1

µµµµ