Rainbow Electronics DS1822 - Manual (Page 15)

DS1822
15 of 20
The DS1822 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 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
2
[B8h] commands to find out the status
of the operation as explained in the DS1822 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 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
µµµµ
s 15
µµµµ
s
V
PU
GND
1-WIRE BUS
60 µµµµ s < T
X
“0” < 120
1
µµµµ
s < T
REC
<
∞
DS1822 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
DS1822 Samples
MIN TYP MAX
LINE TYPE LEGEND
Bus master pulling low DS1822 pulling low
Resistor pullup
> 1 µµµµ s