Read/write time slot timing diagram figure 14, Read time slots – Rainbow Electronics DS18B20X User Manual
Page 15
DS18B20X
15 of 21
The DS18B20X samples the 1-wire bus during a window that lasts from 15
µ
s to 60
µ
s 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
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 E
2
[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
µ
s in duration with a minimum of a 1
µ
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
µ
s 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
µ
s after the falling edge that initiated the read time slot.
45
µµµµ
s
15
µµµµ
s
V
PU
GND
1-WIRE BUS
60
µµµµ
s < T
X
“0” < 120
1
µµµµ
s < T
REC
<
∞
DS18B20X
Samples
MIN TYP MAX
15
µµµµ
s
30
µµµµ
s
> 1
µµµµ
s
MASTER WRITE “0” SLOT
MASTER WRITE “1” SLOT
V
PU
GND
1-WIRE BUS
15
µµµµ
s
MASTER READ “0” SLOT
MASTER READ “1” SLOT
Master samples
Master samples
START
OF SLOT
START
OF SLOT
> 1
µµµµ
s
1
µµµµ
s < T
REC
<
∞
15
µµµµ
s
15
µµµµ
s
30
µµµµ
s
15
µµµµ
s
DS18B20X
Samples
MIN TYP MAX
LINE TYPE LEGEND
Bus master pulling low
DS18B20X pulling low
Resistor
pullup
> 1
µµµµ
s