DS18B20-SL DALLAS [Dallas Semiconductor], DS18B20-SL Datasheet - Page 16

• Manufacturer Part Number: DS18B20-SL
• Description: Programmable Resolution 1-Wire Digital Thermometer
• Manufacturer: DALLAS [Dallas Semiconductor]

The DS18B20 samples the 1-Wire bus during a window that lasts from 15μs 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 DS18B20.
If the line is low, a 0 is written to the DS18B20.
Figure 14. Read/Write Time Slot Timing Diagram
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
of the operation as explained in the DS18B20 Function Commands section.
All read time slots must be a minimum of 60μs 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 1μs 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
1-WIRE BUS
1-WIRE BUS
V
GND
V
GND
PU
PU
> 1μs
OF SLOT
START
15μs
15μs
LINE TYPE LEGEND
MASTER WRITE “0” SLOT
MASTER READ “0” SLOT
60μs < T
MIN
Master samples
15μs
Bus master pulling low
Resistor pullup
DS18B20 Samples
X
“0” < 120μs
TYP
45μs
30μs
16 of 22
MAX
> 1 μs
OF SLOT
START
DS18B20 pulling low
15μs
15μs
1μs < T
1μs < T
2
[B8h] commands to find out the status
MASTER WRITE “1” SLOT
> 1μs
MASTER READ “1” SLOT
REC
REC
MIN
<
<
∞
∞
Master samples
15μs
DS18B20 Samples
TYP
30μs
MAX
DS18B20