DS18B20X
The DS18B20X 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
DS18B20X. If the line is low, a 0 is written to the DS18B20X.
READ/WRITE TIME SLOT TIMING DIAGRAM Figure 14
START
OF SLOT
START
OF SLOT
MASTER WRITE “0” SLOT
MASTER WRITE “1” SLOT
1 µs < TREC < ∞
60 µs < TX “0” < 120
> 1 µs
VPU
1-WIRE BUS
GND
DS18B20X Samples
DS18B20X Samples
MIN
TYP
MAX
MIN
TYP
MAX
15 µs
15 µs
15 µs
15 µs
30 µs
30 µs
MASTER READ “0” SLOT
MASTER READ “1” SLOT
1 µs < TREC < ∞
VPU
1-WIRE BUS
GND
> 1 µs
Master samples
Master samples
> 1 µs
15 µs
45 µs
15 µs
LINE TYPE LEGEND
Bus master pulling low
DS18B20X pulling low
Resistor pullup
READ TIME SLOTS
The DS18B20X 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 DS18B20X can provide the requested data. In addition, the
master can generate read time slots after issuing Convert T [44h] or Recall E2 [B8h] commands to find
out the status of the operation as explained in the DS18B20X 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 DS18B20X will begin transmitting a 1 or 0 on bus. The DS18B20X transmits a 1 by leaving the bus
high and transmits a 0 by pulling the bus low. When transmitting a 0, the DS18B20X 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 DS18B20X is valid for 15 µs after the falling edge that initiated the read time slot.
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DALLAS [ DALLAS SEMICONDUCTOR ]
