DS1822

16 of 21

The DS1822 samples the 1-Wire bus during a window that lasts from 15

μs to 60μs after the master

initiates the write time slot. If the bus is high during the sampling window, a 1 is written to the DS1822.

If the line is low, a 0 is written to the DS1822.

READ/WRITE TIME SLOT TIMING DIAGRAM Figure 14

READ TIME SLOTS

The DS1822 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 DS1822 can provide the requested data. In addition, the master can

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

of the operation as explained in the DS1822 FUNCTION COMMAND section.

All read time slots must be a minimum of 60

μs in duration with a minimum of a 1μs 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 DS1822 will begin transmitting a 1 or 0 on bus. The DS1822 transmits a 1 by leaving the bus high

and transmits a 0 by pulling the bus low. When transmitting a 0, the DS1822 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

45

μs

15

μs

GND

1-WIRE BUS

60

μs < T

1

μs < T

∞

DS1822 Samples

MIN

TYP

MAX

15

μs

30

μs

> 1

μs

MASTER WRITE “0” SLOT

MASTER WRITE “1” SLOT

GND

1-WIRE BUS

15

μs

MASTER READ “0” SLOT

MASTER READ “1” SLOT

Master samples

Master samples

START

OF SLOT

START

OF SLOT

> 1

μs

1

μs < T

∞

15

μs

15

μs

30

μs

15

μs

DS1822 Samples

MIN

TYP

MAX

LINE TYPE LEGEND

Bus master pulling low

DS1822 pulling low

Resistor pullup

> 1

μs